2. TOPICS :
Definitions
Data and types of data
Methods of data presentations
Types of stats
Measure of central tendency
Measure of dispersions
The normal distribution
2
4. STATISTICS: Principles and methods for collection,
presentation, analysis and interpretation of data.
BIOSTATISTICS: Tools of statistics applied to the data that
is derived from biological sciences.
4
5. WHY DO WE NEED
BIOSTATISTICS ?
To define normalcy.
To study the correlation or association between two or more
attributes.
Locate define and measure the extent of the disease.
To evaluate the efficacy of drugs.
To determine the success or failure of health care program.
5
7. DESCRIPTIVE AND
INFERENTIAL STATISTICS
Descriptive stats are concerned with the presentation,
organisation, and summarization of data.
Inferential stats allow us to generalise from our sample
group of data to a larger group of subjects.
7
9. FLAVOURS OF VARIABLES
DEPENDENT variable is the outcome of interest, which
should change in response to some intervention.
INDEPENDENT variable is the intervention, or what is being
manipulated.
9
10. More generally if one variable changes in response to
another, we say that dependent variable is the one that
changes in response to independent variable.
10
19. RATIO SCALE
A ratio scale has equal interval between values and a
meaningful zero point.
19
20. SCALES AT GLANCE
20
Scale type Assumptions
Nominal
NAMED
categories
Ordinal
Ordered
categories
Interval Equal intervals
Ratio Meaningful zero
21. EXAMPLES OF SCALES
Indicate whether the following variables are nominal, ordinal, interval or
ratio.
a) your income (assuming it's more than $0).
b) a list of the different specialities in your profession.
c) the ranking of specialities with regard to income.
d) Salman Khan was described as a "10". What type of variable was
the scale?
e) a range of motion in degrees.
21
22. EXAMPLES OF SCALES
f) a score of 13 out of 17 on the Anxiety Scale.
g) staging of breast cancer as type I, II, III or IV.
h) ST depression on the ECG, measured in millimeters.
i) ST depression, measured as "1"+/- 1mm, "2"= 1 to 5mm, and "3" </=
5mm.
j) ICD-9 classifications: 0295=organic psychosis, 0296=depression and
so on.
k) diastolic blood pressure , in mm Hg.
l) pain measurement on a seven-point scale 22
23. PROPORTION AND RATE
A proportion is a type of fraction in which the numerator is
subset of the denominator.
Rate is a fraction that also has a time component.
23
36. FOR MAKING HISTOGRAMS
Rank order the data
Find the range
Choose the width
New table giving you interval midpoint count etc
Turn into histogram
Lose some info on the way
36
45. SO WHEN TO USE WHAT ?
Bar graphs and Histograms can be used for all types of
data.
But when more than 2 groups than frequency polygon.
Use graphs to show relationships not to report
numbers.
45
52. NUMBERS
A specific data point - the value of variable for one subject is
represented by capital letter X.
We denote the mean of a variable by putting a bar over the
capital letter X: X
The number of subjects in the sample is represented by N.
n indicates the sample size of a group.
Use subscript notation to differentiate between various sample
sizes data points etc.
52
55. INTERVAL AND RATIO DATA
Mean is the measure of central tendency.
A measure of central tendency is the typical value for the
data.
55
56. ORDINAL DATA
Median is the measure of central tendency.
The median is that value such that half of the data points fall
above it half below it .
56
57. NOMINAL DATA
Mode is the measure of central tendency.
The mode is the most frequently occurring category.
57
68. N/C: SETTING THE SCENE
A survey of schools found that the most widely used method
to get out of going to school is "not today mom I have a
headache". Based on the survey of 2000 student it was
found to be used an average of 100 times a year with a SD
of 15. Can we determine what proportion of students use
this reason at least 115 times a year; or fewer than 70 times
a year; or between 106 and 112 times annually ?
68
Also for planning and administration of health care services.
Predicting the trends of the diseases.
To assess health status of population.
To understand the association between cause and effect in various diseases.
To assess the efficacy of various treatments for those diseases.
Ordinal/ interval
Staging is ordinal
St depression is ratio
Grouping ordinal
List diagnosis is nominal
Bp is ratio
Ordinal treated as interval
M bar IS also used
To add series of numbers we use uppercase Greek letter sigma