levels of measurement

Question 1

What are the four levels of measurement in psychology?

Answer 1

• Nominal
• Ordinal
• Interval

Question 2

What is nominal data?

Answer 2

Nominal data is categorical data placed into discrete categories with no intrinsic order (e.g., types of pet, gender, favourite colour).

Question 3

What is ordinal data?

Answer 3

Ordinal data can be ranked or placed in order, but the intervals between values are not equal (e.g., finishing positions in a race, rating scales from 1–10).

Question 4

What is interval data?

Answer 4

Interval data has equal, measurable intervals between values and no true zero (e.g., temperature in °C). It’s considered most statistically powerful of the three AQA-relevant levels.

Question 5

How can you tell the difference between ordinal and interval data?

Answer 5

• Ordinal: ranks without precise equal intervals (e.g., happiness ratings)
• Interval: precise measurements with equal intervals (e.g., test scores, time on stopwatch)

Question 6

Why are levels of measurement important in psychology?

Answer 6

They determine which descriptive statistics (e.g. median, mean) and statistical tests (e.g. Mann-Whitney vs. t-test) are appropriate for data analysis.

Question 7

What descriptive statistics are suitable for each level of measurement?

Answer 7

• Nominal – Mode
• Ordinal – Median (and mode)
• Interval – Mean, Median, Mode, Standard Deviation

Question 8

Give an example of each level of measurement.

Answer 8

• Nominal: blood type (A, B, AB, O)
• Ordinal: survey satisfaction ratings (1st, 2nd, 3rd)
• Interval: IQ scores, temperature in Celsius

Question 9

How do levels of measurement affect the choice of statistical test?

Answer 9

Each test requires data at a certain level:
• Nominal: Chi-squared
• Ordinal: Sign test, Mann-Whitney, Wilcoxon
• Interval: t-tests, Pearson’s r (if parametric assumptions met)