Variables (Statistics )

1. Introducing Biostatistics:
Variables, Data and Scales of
Measurement
By
Prof M A Hafez
Prof. & Advisor, Dept. of Biostatistics
Bangladesh University of Health Sciences(BUHS)

2. Introducing Biostatistics
Objectives
A the end of the session the students should be able to:
 Define variable, their types and
characteristics;
 State the scales of measurement; illustrate
each scale with appropriate example.

3. Definitions
Statistics has three meanings:
 The subject
 Data
 Summary measure(s)
(computed from sample)
Statistics-the subject:
Deals with collection, analysis and interpretation of data.
Statistics - Data: The term statistics is often interchange-
ably used as data e.g. health manpower statistics.
Statistics – Sample-based summary measure:
Any summary measure worked out using sample data.
for example: sample mean
Biostatistics: Statistics about biological sciences; covers such
fields as Public health, Medicine, Nutrition, genetics etc.

4. Data:
Outcome of variables in respect of group of individuals
Variable:
Variable = Vary + able
Any characteristic or measurement that is able to vary.
Qualitative Variable:
Outcome stated in narrative form e.g.
Sex: Male/Female
Quantitative Variable:
Outcome stated in number or quantity e.g.
Height, Weight etc.
Nature of variable:
Discrete ( e.g. Parity- 0, 1,2….. )
Continuous: Height (e.g. 65.234509 inches)

5. Variable Types & Nature
Variable
Qualitative Quantitative
Discrete
(whole
number)
Continuous
(any value)
Discrete
(whole
number)
Type:
Nature:

6. Scales of Measurement
• Nominal: Name only eg. Sex (male/female)
• Ordinal: Imply order
e.g education (primary/secondary, higher secondary, ……)
• Interval: 0 does not imply absence
Interval between two numbers – meaningful
Ratio between two numbers not meaningful
eg. Temperature
• Ratio: 0 imply absence
Interval between two numbers – meaningful
Ratio between two numbers meaningful
eg. height

7. Variable Types and scales of
measurement
Variable
Qualitative Quantitative
Normal
[name only
no order]
eg.Sex (M/F)
Ordinal
[name + order]
Pain
severity(mild,
mod., severe)
Interval
0 does not implies
absence
Interval meaningful
Ratio not
meaningful
Ratio
0 imply absence
Both Interval and
Ratio meaningful
Scales of Measurements
Type:
Scale:

8. Sample : Part of a population
Population: Totality of all the units
Unit : Smallest entity that has the
Characteristics under study
Symbols representing population and sample
Characteristics population sample
Size N n
Variable X X
Data set x x

9. Practical Exercise
• Fill up the blanks with variable type and Scale. You add two
variables in the list and fill up the blanks:
• Var name Type Nature Scale
• Occupation
• Religion
• Hours of study
• Parity
• Shirt collar size
• Sample size
• Blood group
• Exam score
• Serum creatinine level
• Duration of hospital stay
• Eye colour
• Eye Vision
• Liver size

10. Var name Var type (Qn/Ql) Var nature (D/C) Scale (N/O/I/R)
Occupation Qualitative Discrete Nominal
Religion Qualitative Discrete Nominal
Hours of study Quantitative Continuous Ratio
Parity Quantitative Discrete Ratio
Shirt collar size Quantitative Continuous Ratio
Sample size Quantitative Discrete Ratio
Blood group Qualitative Discrete Nominal
Exam score Quantitative Discrete Interval
Serum creatinine level Quantitative Continuous Ratio
Duration of hospital stay Quantitative Discrete Ratio
Eye colour Qualitative Discrete Nominal
Eye Vision Quantitative Discrete Nominal
Liver size Quantitative Continuous Ratio
Education Qualitative Discrete Ordinal