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Other Tests: Correlation

Measures the extent to which two concepts are related

eg years of university training vs computer ownership per capita

How?

obtain the two sets of measurements

calculate correlation coefficient

+1: positively correlated

 0: no correlation (no relation)

–1: negatively correlated

Dangers

attributing causality

a correlation does not imply cause and effect

cause may be due to a third “hidden” variable related to both other variables

eg (above example) age, affluence

drawing strong conclusion from small numbers

unreliable with small groups

be wary of accepting anything more than the direction of correlation unless you have at least 40 subjects

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