The things that you are interested in measuring are called variables. There are two types:
- Independent variable is not affected by other things. It is independent of other variables.
- Dependent variable is affected by other things. It is dependent on other variables.
An independent variable causes a change in a dependent variable. A dependent variable cannot cause a change in an independent variable.
There are four measurement scales for variables:
- Nominal: variables that are not numerical,
e.g. categories like gender and ethnicity.
- Ordinal: variables where order has meaning, but the difference between values is not important,
e.g. ranks like 1st, 2nd and 3rd.
- Interval: variables where the difference between values is important,
e.g. actual numbers like the temperature in °C.
- Ratio: Iinterval data with a natural (absolute) zero point.
Time in seconds has a ratio scale, but temperature in °C does not (since 0°C does not mean no heat).