Types of Variables in Statistics

Study Notes

Variables are characteristics that change from one subject to another or from thing to thing.
Constants are observations with a defined and unchanging value regardless of the unit or setting (e.g., light speed, gravitational acceleration).
Variables have different values depending on the observation unit or setting (e.g., age, gender, blood pressure, weight, height, fasting blood glucose).

Qualitative variables (categorical) are those where the answer to a question is a category from a list of mutually exclusive categories.
Examples include:
- Blood group (A, B, AB, or O)
- Educational level (illiterate, primary, secondary, university graduate)
- Nationality (Egyptian, English, French)
- Residence (Governorate)

Qualitative variables can be further classified as:
- Nominal: Categories have no natural order (e.g., blood groups, nationality).
- Ordinal: Categories have a natural order (e.g., school attendance: none, primary, high, university; social class: low, middle, high).

Binary variables have only two categories (e.g., sex: male/female; disease: affected/free).

Quantitative variables are observations that can be expressed as numbers.
- Discrete: Whole numbers, counted (e.g., number of children, number of beds in a hospital).
- Continuous: Measured with a fraction using a scale (e.g., height, weight, blood pressure, serum cholesterol).

Equal intervals: The distance between successive measures are equal, but not necessarily proportionate (e.g., temperature). -The difference between 100° and 50° is the same as the difference between 0° and 50°, but 100° doesn't represent double the heat of 50°.
Equal intervals and equal proportion: Successive measurements are equal and proportionate. (e.g., weight)
- A 120 kg person weighs twice as much as a 60 kg person.
True zero: The zero point represents the absence of the quantity (e.g., a weight of zero means there is no weight).