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Pearson Product Moment 
Correlation 
Welcome to the Pearson Product 
Moment Correlation Learning 
Module
• The Pearson Product Moment Correlation is the most 
widely used statistic when determining the 
relationship between two variables that are 
continuous.
• The Pearson Product Moment Correlation is the most 
widely used statistic when determining the 
relationship between two variables that are 
continuous. 
Variable A Variable B
• By continuous we mean a variable that can take any 
valuable between two points.
• By continuous we mean a variable that can take any 
valuable between two points. 
• Here is an example:
• By continuous we mean a variable that can take any 
valuable between two points. 
• Here is an example: 
Suppose the fire department mandates that all fire fighters must 
weigh between 150 and 250 pounds. The weight of a fire fighter 
would be an example of a continuous variable; since a fire 
fighter's weight could take on any value between 150 and 250 
pounds.
• By continuous we mean a variable that can take any 
valuable between two points. 
• Here is an example: 
Suppose the fire department mandates that all fire fighters must 
weigh between 150 and 250 pounds. The weight of a fire fighter 
would be an example of a continuous variable; since a fire 
fighter's weight could take on any value between 150 and 250 
pounds.
• The Pearson Product Moment Correlation will either 
indicate a strong relationship
• The Pearson Product Moment Correlation will either 
indicate a strong relationship 
Variable A Variable B
• Or a weak even nonexistent relationship
• Or a weak even nonexistent relationship 
Variable A Variable B
• Strong relationships can either be positive
• Strong relationships can either be positive 
Variable A Variable B
• Or negative
• Or negative 
Variable A Variable B
• The Pearson Product Moment Correlation or simply 
Pearson Correlation values range from -1.0 to +1.0
• The Pearson Product Moment Correlation or simply 
Pearson Correlation values range from -1.0 to +1.0 
-1 0 +1
• A Pearson Correlation of 1.0 has a perfect positive 
relationship. Note two qualities here:
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength 
• A +1.0 Pearson Correlation’s direction is positive and it’s 
strength is very or perfectly strong.
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength 
• A +1.0 Pearson Correlation’s direction is positive and it’s 
strength is very or perfectly strong. 
• A -1.0 Pearson Correlation’s direction is negative and it’s 
strength is very or perfectly strong.
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength 
• A +1.0 Pearson Correlation’s direction is positive and it’s 
strength is very or perfectly strong. 
• A -1.0 Pearson Correlation’s direction is negative and it’s 
strength is very or perfectly strong. 
• A 0.0 Pearson Correlation has no direction and has no 
strength.
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength 
• A +1.0 Pearson Correlation’s direction is positive and it’s 
strength is very or perfectly strong. 
• A -1.0 Pearson Correlation’s direction is negative and it’s 
strength is very or perfectly strong. 
• A 0.0 Pearson Correlation has no direction and has no 
strength. 
• A +0.3 Pearson Correlation’s direction is positive and it’s 
strength is moderately weak.
• A Pearson Correlation of 1.0 has a perfect postive 
relationship. Note two qualities here: 
(1) direction 
(2) strength 
• A +1.0 Pearson Correlation’s direction is positive and it’s 
strength is very or perfectly strong. 
• A -1.0 Pearson Correlation’s direction is negative and it’s 
strength is very or perfectly strong. 
• A 0.0 Pearson Correlation has no direction and has no 
strength. 
• A +0.3 Pearson Correlation’s direction is positive and it’s 
strength is moderately weak. 
• A -0.1 Pearson Correlation’s direction is negative and it’s 
strength is very weak.
• There is another quality as well. With a Pearson 
correlation you are considering the relationship 
between only two variables.
• There is another quality as well. With a Pearson 
correlation you are considering the relationship 
between only two variables.
• There is another quality as well. With a Pearson 
correlation you are considering the relationship 
between only two variables. 
• Three’s a crowd:
• There is another quality as well. With a Pearson 
correlation you are considering the relationship 
between only two variables. 
• Three’s a crowd:
• There is another quality as well. With a Pearson 
correlation you are considering the relationship 
between only two variables. 
• Three’s a crowd: 
• Bottom line: The Pearson Correlation is used only when 
exploring the relationship between two variables.
• Let’s look at a fictitious problem to illustrate how the 
Pearson Correlation is calculated.
• Imagine you are conducting a study to determine the 
relationship between the average daily temperature 
and the average daily ice cream sales in a particular 
city.
• Imagine you are conducting a study to determine the 
relationship between the average daily temperature 
and the average daily ice cream sales in a particular 
city.
• Imagine the data set looks like this:
• Imagine the data set looks like this: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• Notice how as one variable goes up (temperature) 
the other variable increases (ice cream sales)
• Notice how as one variable goes up (temperature) 
the other variable increases (ice cream sales) 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• Notice how as one variable goes up (temperature) 
the other variable increases (ice cream sales) 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• One way to look at this relationship is to rank order 
both variable values like so:
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 2nd
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
3rd 3rd 
2nd
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
3rd 3rd 
2nd 
4th 4th
• One way to look at this relationship is to rank order 
both variable values like so: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Meaning that higher values for one 
variable are associated with higher 
values for another variable
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Meaning that higher values for one 
variable are associated with higher 
values for another variable
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Meaning that higher values for one 
variable are associated with higher 
values for another variable
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Or
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Meaning that lower values for one 
variable are associated with lower 
values for another variable
• Notice how their rank orders are identical. And 
because their standard deviations are similar as well, 
these variables have a +1.0 Pearson Correlation. 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
1st 1st 
2nd 
2nd 
3rd 3rd 
4th 4th 
5th 5th 
Meaning that lower values for one 
variable are associated with lower 
values for another variable
• What would a perfectly negative correlation (-1.0) 
look like?
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd 
Meaning that higher values for one 
variable are associated with lower 
values for another variable
• What would a perfectly negative correlation (-1.0) 
look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
230 
320 
350 
480 
560 
1st 
1st 
2nd 
5th 
5th 
4th 
4th 
3rd 3rd 
2nd 
Meaning that higher values for one 
variable are associated with lower 
values for another variable
• What would a zero correlation (0.0) look like?
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
1st 
1st 
2nd 
4th 
4th 
3rd 
3rd 
2nd
• What would a zero correlation (0.0) look like? 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
5th 5th 
2nd 
1st 
4th 
3rd 
2nd 
1st 
4th 
3rd 
• Note – Pearson Correlation is not just a comparison of rank ordered data 
(that is what a Phi coefficient does) but the rank order is one factor that is 
considered with a Pearson Correlation. Another factor is the degree to 
which the standard deviations are similar.
• The Pearson Product Moment Correlation (PPMC) is 
calculated as the average cross product of the z-scores 
of two variables for a single group of people. 
Here is the equation for the PPMC
• The Pearson Product Moment Correlation (PPMC) is 
calculated as the average cross product of the z-scores 
of two variables for a single group of people. 
Here is the equation for the PPMC 
푟 = Σ (푍푋 ∙ 푍푌) 
푛
• Let’s calculate the Pearson Correlation, for the 
following data set:
• Let’s calculate the Pearson Correlation, for the 
following data set: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• Let’s calculate the Pearson Correlation, for the 
following data set: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
• It is very important to note that the Pearson Correlation 
can be computed in a matter of seconds using statistical 
software. The next set of slides is designed to help you 
see what is happening conceptually as well as 
computationally with the Pearson Correlation.
• When computing a Pearson Correlation you will 
normally have two variables that DO NOT USE THE 
SAME METRIC:
• When computing a Pearson Correlation you will 
normally have two variables that DO NOT USE THE 
SAME METRIC: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• When computing a Pearson Correlation you will 
normally have two variables that DO NOT USE THE 
SAME METRIC: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
The metric 
here is degrees
• When computing a Pearson Correlation you will 
normally have two variables that DO NOT USE THE 
SAME METRIC: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
The metric here is 
number of ice 
cream sales 
The metric 
here is degrees
• So we have to get these two variables on the same 
metric. This is done by calculating the z scores or 
standardized scores for the values from each 
variable.
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric:
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
Different Metric 
(raw scores)
• So these raw score values in separate metrics are 
transformed into standardized values which 
converts them into the same metric: 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
Same Metric 
(z or standard 
scores)
• Note – this is done by subtracting each value from 
it’s mean (e.g., 900 minus 700 = 200) and dividing it 
by it’s standard deviation (e.g., 200 / 14.1 = 1.4) 
Ave Daily Temp 
900 
800 
700 
600 
500 
Ave Daily Ice Cream Sales 
560 
480 
350 
320 
230 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3
• Once the values are standardized we multiply them
• Once the values are standardized we multiply them 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Once the values are standardized we multiply them 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Once the values are standardized we multiply them 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Once the values are standardized we multiply them 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
X 
X 
X 
X 
X 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Once the values are standardized we multiply them 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
X 
X 
X 
X 
X 
Cross Products 
1.9 
0.4 
0.0 
0.6 
2.1 
= 
= 
= 
= 
= 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Once the values are standardized we multiply them 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
X 
X 
X 
X 
X 
Cross Products 
1.9 
0.4 
0.0 
0.6 
2.1 
= 
= 
= 
= 
= 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛 
These are called cross products 
because we are multiplying 
across two values
• Once the values are standardized we multiply them 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
X 
X 
X 
X 
X 
Cross Products 
1.9 
0.4 
0.0 
0.6 
2.1 
= 
= 
= 
= 
= 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛 
1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 5.0 
Then we sum the cross products
• Finally, divide that number (5.0) by the number of 
observations
• Finally, divide that number (5.0) by the number of 
observations 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛
• Finally, divide that number (5.0) by the number of 
observations 
푟 = 
Σ (풁푿 ∙ 풁풀) 
푛 
The number of observations 
(in this case 5) 
Ave Daily Temp 
+1.4 
+0.7 
0.0 
-0.7 
-1.4 
Ave Daily Ice Cream Sales 
+1.5 
+0.8 
-0.3 
-0.6 
-1.3 
1 
2 
3 
4 
5
푟 = 
Σ (풁푿 ∙ 풁풀) 
ퟓ
푟 = 
Σ (풁푿 ∙ 풁풀) 
ퟓ 
The number of observations 
(in this case 5) 
푟 = 
ퟓ 
ퟓ
푟 = 
Σ (풁푿 ∙ 풁풀) 
ퟓ 
The number of observations 
(in this case 5) 
푟 = 
ퟓ 
ퟓ 
Sum of the cross products 
1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 
5.0
푟 = 
Σ (풁푿 ∙ 풁풀) 
ퟓ 
The number of observations 
(in this case 5) 
푟 = 
ퟓ 
ퟓ 
Sum of the cross products 
1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 
5.0 
푟 = +ퟏ. ퟎ
푟 = 
Σ (풁푿 ∙ 풁풀) 
ퟓ 
The number of observations 
(in this case 5) 
푟 = 
ퟓ 
ퟓ 
Sum of the cross products 
1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 
5.0 
푟 = +ퟏ. ퟎ 
This is the Pearson Correlation 
which in this case is a perfect 
positive relationship
• In summary:
• In summary: 
• The Pearson Product Moment Correlation can range 
from -1 to 0 to +1.
• In summary: 
• The Pearson Product Moment Correlation can range 
from -1 to 0 to +1. 
-1 0 +1
• A correlation of 0 indicates no association between 
the variables of interest.
• A correlation of 0 indicates no association between 
the variables of interest. 
• The direction (positive or negative) simply indicates a 
positive or negative (inverse) relationship between 
the variables.
• If POSITIVE, when values increase on one variable, 
they tend to increase on another variable.
• If POSITIVE, when values increase on one variable, 
they tend to increase on another variable. 
Variable 1 
10 
9 
8 
7 
Variable 2 
5 
4 
3 
2 
-1 0 +1
• If POSITIVE, when values increase on one variable, 
they tend to increase on another variable. 
Variable 1 
10 
9 
8 
7 
Variable 2 
5 
4 
3 
2 
-1 0 +1
• If POSITIVE, when values increase on one variable, 
they tend to increase on another variable. 
Variable 1 
10 
9 
8 
7 
Variable 2 
5 
4 
3 
2 
Pearson 
Correlation = +1.0 
-1 0 +1
• If NEGATIVE, when values increase on one variable, 
they tend to decrease on another variable.
• If NEGATIVE, when values increase on one variable, 
they tend to decrease on another variable. 
Variable 1 
10 
9 
8 
7 
Variable 2 
2 
3 
4 
5 
-1 0 +1
• If NEGATIVE, when values increase on one variable, 
they tend to decrease on another variable. 
Variable 1 
10 
9 
8 
7 
Variable 2 
2 
3 
4 
5 
Pearson 
Correlation = -1.0 
-1 0 +1
• The strength of the relationship depends on the 
decimal value.
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
-1 0 0.2 +1 
weak
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
-1 0 0.8 +1 
strong
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
0.2 
weak 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
0.8 
strong 
-1 0 +1
• The strength of the relationship depends on the 
decimal value. 
-1 0 +1
• There is a tendency to interpret the Pearson Product 
Moment Correlation with causal language as though 
changes in one variable causes changes in the other.
• There is a tendency to interpret the Pearson Product 
Moment Correlation with causal language as though 
changes in one variable causes changes in the other. 
• Whether to interpret the Pearson Product Moment 
Correlation as prediction or causation depends on 
the nature of the research design rather than the 
nature of the statistic.
• There is a tendency to interpret the Pearson Product 
Moment Correlation with causal language as though 
changes in one variable causes changes in the other. 
• Whether to interpret the Pearson Product Moment 
Correlation as prediction or causation depends on 
the nature of the research design rather than the 
nature of the statistic. 
• First, analyze the nature of the research design 
before interpreting the Pearson Product Moment 
Correlation with causal or prediction language.
• There is a tendency to interpret the Pearson Product 
Moment Correlation with causal language as though 
changes in one variable causes changes in the other. 
• Whether to interpret the Pearson Product Moment 
Correlation as prediction or causation depends on 
the nature of the research design rather than the 
nature of the statistic. 
• First, analyze the nature of the research design 
before interpreting the Pearson Product Moment 
Correlation with causal or prediction language. 
• So, if your research question is focused on the 
relationship between two continuous variables the 
Pearson Product Moment Correlation would be the 
appropriate statistical method to use.

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  • 1. Pearson Product Moment Correlation Welcome to the Pearson Product Moment Correlation Learning Module
  • 2. • The Pearson Product Moment Correlation is the most widely used statistic when determining the relationship between two variables that are continuous.
  • 3. • The Pearson Product Moment Correlation is the most widely used statistic when determining the relationship between two variables that are continuous. Variable A Variable B
  • 4. • By continuous we mean a variable that can take any valuable between two points.
  • 5. • By continuous we mean a variable that can take any valuable between two points. • Here is an example:
  • 6. • By continuous we mean a variable that can take any valuable between two points. • Here is an example: Suppose the fire department mandates that all fire fighters must weigh between 150 and 250 pounds. The weight of a fire fighter would be an example of a continuous variable; since a fire fighter's weight could take on any value between 150 and 250 pounds.
  • 7. • By continuous we mean a variable that can take any valuable between two points. • Here is an example: Suppose the fire department mandates that all fire fighters must weigh between 150 and 250 pounds. The weight of a fire fighter would be an example of a continuous variable; since a fire fighter's weight could take on any value between 150 and 250 pounds.
  • 8. • The Pearson Product Moment Correlation will either indicate a strong relationship
  • 9. • The Pearson Product Moment Correlation will either indicate a strong relationship Variable A Variable B
  • 10. • Or a weak even nonexistent relationship
  • 11. • Or a weak even nonexistent relationship Variable A Variable B
  • 12. • Strong relationships can either be positive
  • 13. • Strong relationships can either be positive Variable A Variable B
  • 15. • Or negative Variable A Variable B
  • 16. • The Pearson Product Moment Correlation or simply Pearson Correlation values range from -1.0 to +1.0
  • 17. • The Pearson Product Moment Correlation or simply Pearson Correlation values range from -1.0 to +1.0 -1 0 +1
  • 18. • A Pearson Correlation of 1.0 has a perfect positive relationship. Note two qualities here:
  • 19. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction
  • 20. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength
  • 21. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength • A +1.0 Pearson Correlation’s direction is positive and it’s strength is very or perfectly strong.
  • 22. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength • A +1.0 Pearson Correlation’s direction is positive and it’s strength is very or perfectly strong. • A -1.0 Pearson Correlation’s direction is negative and it’s strength is very or perfectly strong.
  • 23. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength • A +1.0 Pearson Correlation’s direction is positive and it’s strength is very or perfectly strong. • A -1.0 Pearson Correlation’s direction is negative and it’s strength is very or perfectly strong. • A 0.0 Pearson Correlation has no direction and has no strength.
  • 24. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength • A +1.0 Pearson Correlation’s direction is positive and it’s strength is very or perfectly strong. • A -1.0 Pearson Correlation’s direction is negative and it’s strength is very or perfectly strong. • A 0.0 Pearson Correlation has no direction and has no strength. • A +0.3 Pearson Correlation’s direction is positive and it’s strength is moderately weak.
  • 25. • A Pearson Correlation of 1.0 has a perfect postive relationship. Note two qualities here: (1) direction (2) strength • A +1.0 Pearson Correlation’s direction is positive and it’s strength is very or perfectly strong. • A -1.0 Pearson Correlation’s direction is negative and it’s strength is very or perfectly strong. • A 0.0 Pearson Correlation has no direction and has no strength. • A +0.3 Pearson Correlation’s direction is positive and it’s strength is moderately weak. • A -0.1 Pearson Correlation’s direction is negative and it’s strength is very weak.
  • 26. • There is another quality as well. With a Pearson correlation you are considering the relationship between only two variables.
  • 27. • There is another quality as well. With a Pearson correlation you are considering the relationship between only two variables.
  • 28. • There is another quality as well. With a Pearson correlation you are considering the relationship between only two variables. • Three’s a crowd:
  • 29. • There is another quality as well. With a Pearson correlation you are considering the relationship between only two variables. • Three’s a crowd:
  • 30. • There is another quality as well. With a Pearson correlation you are considering the relationship between only two variables. • Three’s a crowd: • Bottom line: The Pearson Correlation is used only when exploring the relationship between two variables.
  • 31. • Let’s look at a fictitious problem to illustrate how the Pearson Correlation is calculated.
  • 32. • Imagine you are conducting a study to determine the relationship between the average daily temperature and the average daily ice cream sales in a particular city.
  • 33. • Imagine you are conducting a study to determine the relationship between the average daily temperature and the average daily ice cream sales in a particular city.
  • 34. • Imagine the data set looks like this:
  • 35. • Imagine the data set looks like this: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 36. • Notice how as one variable goes up (temperature) the other variable increases (ice cream sales)
  • 37. • Notice how as one variable goes up (temperature) the other variable increases (ice cream sales) Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 38. • Notice how as one variable goes up (temperature) the other variable increases (ice cream sales) Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 39. • One way to look at this relationship is to rank order both variable values like so:
  • 40. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 41. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st
  • 42. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st
  • 43. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st
  • 44. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd
  • 45. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 3rd 3rd 2nd
  • 46. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 3rd 3rd 2nd 4th 4th
  • 47. • One way to look at this relationship is to rank order both variable values like so: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th
  • 48. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th
  • 49. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Meaning that higher values for one variable are associated with higher values for another variable
  • 50. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Meaning that higher values for one variable are associated with higher values for another variable
  • 51. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Meaning that higher values for one variable are associated with higher values for another variable
  • 52. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Or
  • 53. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Meaning that lower values for one variable are associated with lower values for another variable
  • 54. • Notice how their rank orders are identical. And because their standard deviations are similar as well, these variables have a +1.0 Pearson Correlation. Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 1st 1st 2nd 2nd 3rd 3rd 4th 4th 5th 5th Meaning that lower values for one variable are associated with lower values for another variable
  • 55. • What would a perfectly negative correlation (-1.0) look like?
  • 56. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd
  • 57. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd
  • 58. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd
  • 59. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd
  • 60. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd
  • 61. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd Meaning that higher values for one variable are associated with lower values for another variable
  • 62. • What would a perfectly negative correlation (-1.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 230 320 350 480 560 1st 1st 2nd 5th 5th 4th 4th 3rd 3rd 2nd Meaning that higher values for one variable are associated with lower values for another variable
  • 63. • What would a zero correlation (0.0) look like?
  • 64. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 65. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 66. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 67. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 68. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 69. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 1st 1st 2nd 4th 4th 3rd 3rd 2nd
  • 70. • What would a zero correlation (0.0) look like? Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 5th 5th 2nd 1st 4th 3rd 2nd 1st 4th 3rd • Note – Pearson Correlation is not just a comparison of rank ordered data (that is what a Phi coefficient does) but the rank order is one factor that is considered with a Pearson Correlation. Another factor is the degree to which the standard deviations are similar.
  • 71. • The Pearson Product Moment Correlation (PPMC) is calculated as the average cross product of the z-scores of two variables for a single group of people. Here is the equation for the PPMC
  • 72. • The Pearson Product Moment Correlation (PPMC) is calculated as the average cross product of the z-scores of two variables for a single group of people. Here is the equation for the PPMC 푟 = Σ (푍푋 ∙ 푍푌) 푛
  • 73. • Let’s calculate the Pearson Correlation, for the following data set:
  • 74. • Let’s calculate the Pearson Correlation, for the following data set: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 75. • Let’s calculate the Pearson Correlation, for the following data set: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 • It is very important to note that the Pearson Correlation can be computed in a matter of seconds using statistical software. The next set of slides is designed to help you see what is happening conceptually as well as computationally with the Pearson Correlation.
  • 76. • When computing a Pearson Correlation you will normally have two variables that DO NOT USE THE SAME METRIC:
  • 77. • When computing a Pearson Correlation you will normally have two variables that DO NOT USE THE SAME METRIC: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 78. • When computing a Pearson Correlation you will normally have two variables that DO NOT USE THE SAME METRIC: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 The metric here is degrees
  • 79. • When computing a Pearson Correlation you will normally have two variables that DO NOT USE THE SAME METRIC: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 The metric here is number of ice cream sales The metric here is degrees
  • 80. • So we have to get these two variables on the same metric. This is done by calculating the z scores or standardized scores for the values from each variable.
  • 81. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric:
  • 82. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 83. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230
  • 84. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3
  • 85. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 Different Metric (raw scores)
  • 86. • So these raw score values in separate metrics are transformed into standardized values which converts them into the same metric: Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 Same Metric (z or standard scores)
  • 87. • Note – this is done by subtracting each value from it’s mean (e.g., 900 minus 700 = 200) and dividing it by it’s standard deviation (e.g., 200 / 14.1 = 1.4) Ave Daily Temp 900 800 700 600 500 Ave Daily Ice Cream Sales 560 480 350 320 230 Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3
  • 88. • Once the values are standardized we multiply them
  • 89. • Once the values are standardized we multiply them 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 90. • Once the values are standardized we multiply them 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 91. • Once the values are standardized we multiply them Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 92. • Once the values are standardized we multiply them Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 X X X X X 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 93. • Once the values are standardized we multiply them Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 X X X X X Cross Products 1.9 0.4 0.0 0.6 2.1 = = = = = 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 94. • Once the values are standardized we multiply them Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 X X X X X Cross Products 1.9 0.4 0.0 0.6 2.1 = = = = = 푟 = Σ (풁푿 ∙ 풁풀) 푛 These are called cross products because we are multiplying across two values
  • 95. • Once the values are standardized we multiply them Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 X X X X X Cross Products 1.9 0.4 0.0 0.6 2.1 = = = = = 푟 = Σ (풁푿 ∙ 풁풀) 푛 1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 5.0 Then we sum the cross products
  • 96. • Finally, divide that number (5.0) by the number of observations
  • 97. • Finally, divide that number (5.0) by the number of observations 푟 = Σ (풁푿 ∙ 풁풀) 푛
  • 98. • Finally, divide that number (5.0) by the number of observations 푟 = Σ (풁푿 ∙ 풁풀) 푛 The number of observations (in this case 5) Ave Daily Temp +1.4 +0.7 0.0 -0.7 -1.4 Ave Daily Ice Cream Sales +1.5 +0.8 -0.3 -0.6 -1.3 1 2 3 4 5
  • 99. 푟 = Σ (풁푿 ∙ 풁풀) ퟓ
  • 100. 푟 = Σ (풁푿 ∙ 풁풀) ퟓ The number of observations (in this case 5) 푟 = ퟓ ퟓ
  • 101. 푟 = Σ (풁푿 ∙ 풁풀) ퟓ The number of observations (in this case 5) 푟 = ퟓ ퟓ Sum of the cross products 1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 5.0
  • 102. 푟 = Σ (풁푿 ∙ 풁풀) ퟓ The number of observations (in this case 5) 푟 = ퟓ ퟓ Sum of the cross products 1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 5.0 푟 = +ퟏ. ퟎ
  • 103. 푟 = Σ (풁푿 ∙ 풁풀) ퟓ The number of observations (in this case 5) 푟 = ퟓ ퟓ Sum of the cross products 1.9 + 0.4 + 0.0 + 0.6 + 2.1 = 5.0 푟 = +ퟏ. ퟎ This is the Pearson Correlation which in this case is a perfect positive relationship
  • 105. • In summary: • The Pearson Product Moment Correlation can range from -1 to 0 to +1.
  • 106. • In summary: • The Pearson Product Moment Correlation can range from -1 to 0 to +1. -1 0 +1
  • 107. • A correlation of 0 indicates no association between the variables of interest.
  • 108. • A correlation of 0 indicates no association between the variables of interest. • The direction (positive or negative) simply indicates a positive or negative (inverse) relationship between the variables.
  • 109. • If POSITIVE, when values increase on one variable, they tend to increase on another variable.
  • 110. • If POSITIVE, when values increase on one variable, they tend to increase on another variable. Variable 1 10 9 8 7 Variable 2 5 4 3 2 -1 0 +1
  • 111. • If POSITIVE, when values increase on one variable, they tend to increase on another variable. Variable 1 10 9 8 7 Variable 2 5 4 3 2 -1 0 +1
  • 112. • If POSITIVE, when values increase on one variable, they tend to increase on another variable. Variable 1 10 9 8 7 Variable 2 5 4 3 2 Pearson Correlation = +1.0 -1 0 +1
  • 113. • If NEGATIVE, when values increase on one variable, they tend to decrease on another variable.
  • 114. • If NEGATIVE, when values increase on one variable, they tend to decrease on another variable. Variable 1 10 9 8 7 Variable 2 2 3 4 5 -1 0 +1
  • 115. • If NEGATIVE, when values increase on one variable, they tend to decrease on another variable. Variable 1 10 9 8 7 Variable 2 2 3 4 5 Pearson Correlation = -1.0 -1 0 +1
  • 116. • The strength of the relationship depends on the decimal value.
  • 117. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 118. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 119. • The strength of the relationship depends on the decimal value. -1 0 0.2 +1 weak
  • 120. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 121. • The strength of the relationship depends on the decimal value. -1 0 0.8 +1 strong
  • 122. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 123. • The strength of the relationship depends on the decimal value. 0.2 weak -1 0 +1
  • 124. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 125. • The strength of the relationship depends on the decimal value. 0.8 strong -1 0 +1
  • 126. • The strength of the relationship depends on the decimal value. -1 0 +1
  • 127. • There is a tendency to interpret the Pearson Product Moment Correlation with causal language as though changes in one variable causes changes in the other.
  • 128. • There is a tendency to interpret the Pearson Product Moment Correlation with causal language as though changes in one variable causes changes in the other. • Whether to interpret the Pearson Product Moment Correlation as prediction or causation depends on the nature of the research design rather than the nature of the statistic.
  • 129. • There is a tendency to interpret the Pearson Product Moment Correlation with causal language as though changes in one variable causes changes in the other. • Whether to interpret the Pearson Product Moment Correlation as prediction or causation depends on the nature of the research design rather than the nature of the statistic. • First, analyze the nature of the research design before interpreting the Pearson Product Moment Correlation with causal or prediction language.
  • 130. • There is a tendency to interpret the Pearson Product Moment Correlation with causal language as though changes in one variable causes changes in the other. • Whether to interpret the Pearson Product Moment Correlation as prediction or causation depends on the nature of the research design rather than the nature of the statistic. • First, analyze the nature of the research design before interpreting the Pearson Product Moment Correlation with causal or prediction language. • So, if your research question is focused on the relationship between two continuous variables the Pearson Product Moment Correlation would be the appropriate statistical method to use.