Choosing a statistical test

Question 1

intro

Answer 1

In A-level psychology there are 8 statistical tests you need to know.
You won’t need to calculate 7 of them, but you will need to know when to use them.

Question 2

Choosing a test

Answer 2

Choosing a statistical test relies on several pieces of information.
Most of these will be given in the question:
• Test of difference or a correlation
• Test design
• Levels of measurement

Two of these should be a familiar to you.
• Test of difference or a correlation
• Should be obvious from the wording of the hypothesis / question.
Association or relationship = correlation.
• Test design = experimental design.
• Unrelated
→ Independent groups
• Related
Repeated measure or matched pairs.

Question 3

Levels of measurement

Answer 3

Nominal-• Categorical data
• Favourite desert
• Smoker / non-smoker
• Sex
• Discrete data → only appears in 1 category.

Ordinal-Ordinal
• Data that can be ordered in some way.
• E.g. Rating scales.
However=• Subjective
• No equal intervals between values.-Someone’s concept of 2/10 may be different to another’s

This is ordinal data because we can rank the runners from fastest to slowest. However, the time gaps between them are unknown and not necessarily equal:
• Alice might have finished 10 seconds ahead of Bob.
• Bob might have finished just 1 second ahead of Charlie.

Interval data-• Data based on numerical scales.
• E.g. weight, size, scores, speed.
• Objective
• Equal intervals between values.
• Most sophisticated form.

Question 4

Choosing a test

Answer 4

Tod-unrelated, related
Test of correlation/association at end

then nominal at top,then ordinal and then interval-in order of sophistication-interval most sophisticated

Carrots should come mashed with swede under roast potatoes

Chi squared, sign test, chi squared, mann whitney, wilcoxon, spearman’s rho, unrelated t-test, related t test, person’s r

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