2. Common Errors
Not using as intended
Scoring errors
Poor interpretation
Not following rules
No rapport
Poor Documentation during test
Using the quickest test Because we have to
3. Raw Score
• First Score
• Number Correct
Presented by: Brent Daigle, Ph.D. (ABD)
4. Norm Referenced Test
Compares with national average
Presented by: Brent Daigle, Ph.D. (ABD)
10. Normal Distribution
Normal Distribution: Symmetrical , single # for
Mean/Med/Mode
Measures of Central tendency : How # cluster around the mean
Presented by: Brent Daigle, Ph.D. (ABD)
11. Median
Middle value in distribution
1) Arrange data in order 2) Find the middle value
Presented by: Brent Daigle, Ph.D. (ABD)
12. Calculating the Median
(High Temperatures)
High
Date Temperature 42 43
7-Jan 32 median 42.5
8-Jan 32
2
6-Jan 35
10-Jan 41
5-Jan 42 <===Middle values
4-Jan 43 <===Middle values
9-Jan 46
11-Jan 52
2-Jan 59
3-Jan 60
Presented by: Brent Daigle, Ph.D. (ABD)
13. Mean
X
X
n
Add up, divide by number of values
The average
Presented by: Brent Daigle, Ph.D. (ABD)
14. Mode
Not useful with several = values
Does not take into account exact scores
Most frequent value
15. Notice how there are more people (n=6) with a 10 inch right foot than any other length.
Notice also how as the length becomes larger or smaller, there are fewer and fewer people
with that measurement. This is a characteristics of many variables that we measure. There is a
tendency to have most measurements in the middle, and fewer as we approach the high and
low extremes.
If we were to connect the top of each bar, we would create a
8 frequency polygon.
7
6
5
Number of People with
4
3
that Shoe Size
2
1
4 5 6 7 8 9 10 11 12 13 14
Length of Right Foot
16. Presented by: Brent Daigle, Ph.D. (ABD)
You will notice that if we smooth the lines,
our data almost creates a bell shaped
curve.
8
7
6
5
Number of People with
4
3
that Shoe Size
2
1
4 5 6 7 8 9 10 11 12 13 14
Length of Right Foot
17. Presented by: Brent Daigle, Ph.D. (ABD)
You will notice that if we smooth the lines, our data almost creates a bell
shaped curve.
This bell shaped curve is known as the “Bell Curve” or the “Normal
Curve.”
8
7
6
5
Number of People with
4
3
that Shoe Size
2
1
4 5 6 7 8 9 10 11 12 13 14
Length of Right Foot
18. Whenever you see a normal curve, you should
imagine the bar graph within it.
9
8
Number of Students
7
6
5
4
3
2
1
12 13 14 15 16 17 18 19 20 21 22
Points on a Quiz
Presented by: Brent Daigle, Ph.D. (ABD)
19. The mean, mode, will all fall on the same value in a normal distribution.
and median
Now lets look at quiz scores for 51 students. 12
13 13
12+13+13+14+14+14+14+15+15+15+15+15+15+16+16+16+16+16+16+16+16+
12, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 22
17+17+17+17+17+17+17+17+17+18+18+18+18+18+18+18+18+19+19+19+19+ 19+
14 14 14 14
19+20+20+20+20+ 21+21+22 = 867 15 15 15 15 15 15
867 / 51 = 17 16 16 16 16 16 16 16 16
17 17 17 17 17 17 17 17 17
18 18 18 18 18 18 18 18
19 19 19 19 19 19
20 20 20 20
9 21 21
8
22
Number of Students
7
6
5
4
3
2
1
12 13 14 15 16 17 18 19 20 21 22
Points on a Quiz
Presented by: Brent Daigle, Ph.D. (ABD)
20. Normal distributions (bell shaped) are a
family of distributions that have the same
general shape. They are symmetric (the
left side is an exact mirror of the right side)
with scores more concentrated in the
middle than in the tails. Examples of
normal distributions are shown to the
right. Notice that they differ in how spread
out they are. The area under each curve is
the same.
Presented by: Brent Daigle, Ph.D. (ABD)
21. If your data fits a normal distribution, approximately 68% of your subjects will fall
within one standard deviation of the mean.
Approximately 95% of your subjects will fall within two standard deviations of the
mean.
Over 99% of your subjects will fall within three standard deviations of the mean.
Presented by: Brent Daigle, Ph.D. (ABD)
22. The mean and standard deviation are useful ways to describe a set of scores. If
the scores are grouped closely together, they will have a smaller standard
deviation than if they are spread farther apart.
Small Standard Deviation Large Standard Deviation
Click the mouse to view a variety of pairs of normal distributions below.
Same Means Different Means Different Means
Different Standard Deviations Same Standard Deviations Different Standard Deviations
Presented by: Brent Daigle, Ph.D. (ABD)
