Qualitative data are often termed categorical data. Data that can be added into categories according to their characteristics.
Nominal Variable (Unordered list)
A variable that has two or more categories, without any implied ordering.
- Gender – Male, Female
- Marital Status – Unmarried, Married, Divorcee
- State – New Delhi, Haryana, Illinois, Michigan
Ordinal Variable (Ordered list)
A variable that has two or more categories, with clear ordering.
- Scale – Strongly Disagree, Disagree, Neutral, Agree, Strongly Agree
- Rating – Very low, Low, Medium, Great, Very great
An interval variable is similar to an ordinal variable, except that the intervals between the values of the interval variable are equally spaced. In other words, it has order and equal intervals.
- Temperature in Celsius – Temperature of 30°C is higher than 20°C, and temperature of 20°C is higher than 10°C. The size of these intervals is the same.
- Annual Income in Dollars – Three people who make $5,000, $10,000 and $15,000. The second person makes $5,000 more than the first person and $5,000 less than the third person, and the size of these intervals is the same.
It is interval data with a natural zero point. When the variable equals 0.0, there is none of that variable.
- Temperature in Kelvin – It is a ratio variable, as 0.0 Kelvin really does mean ‘no temperature.