Measurement scales: what you may do with a variable
lesson~10 minflashcardsgamequizup to 50 pts
Why the scale matters
You can compute the mean of postal codes. Neither Python nor Excel will object. The result 921 47 is nonsense, though, because a postal code is not a quantity but a label. The measurement scale tells you which calculations make sense for a variable.
| Scale | What the values express | Example | What makes sense |
|---|---|---|---|
| nominal | only different categories | field of study, region, postal code | frequencies, proportions, mode |
| ordinal | categories with an order | education, satisfaction 1 to 5 | also the median and quantiles |
| interval | numbers with measurable differences, zero is a convention | temperature in °C, year of birth | also the mean, standard deviation |
| ratio | numbers with a natural zero | weight, income, number of children | also ratios such as "twice as much" |
The first two are categorical, the last two metric (numeric). Each scale allows everything that the scales above it in the table allow.