2. Sampling and Measurement. Variable – a characteristic that can vary in value among subjects in a sample or a population. Two types of variables: Categorical Quantitative There are different statistical methods for each type of variable.
Two types of variables:
Quantitative variable – possible values differ in magnitude
A characteristic that can vary in value among subjects in a sample or a population.
subject gen age high colltv veg party ideology abor
1 m 32 2.2 3.5 3 n r 6 n
2 f 23 2.1 3.5 15 y d 2 y
3 f 27 3.3 3.0 0 y d 2 y
4 f 35 3.5 3.2 5 n i 4 y
5 M 23 3.1 3.5 6 n i 1 y
Two types of categorical variables:
Note: In practice, ordinal categorical variables often treated as interval by assigning scores
Level of agreement is an ordinal scale, but treated as interval if assigned scores 4=Totally agree, 3=Agree, 2=Disagree ,1=Totally disagree.
Ordering of variable types from highest to lowest level of differentiation among levels:
Discrete variable – possible values a set of separate numbers, such as 0, 1, 2, …
Example: Number of …
e-mail messages sent in previous day
Continuous variable – infinite continuum of possible values
Example: Amount of time spent on Internet in previous day
(In practice, distinction often blurry)
Read pages 19-21 of text for examples