Inferential Statistics and Hypothesis Testing

Descriptive statistics (means, standard deviations, graphs) summarise data but do not tell us whether differences or relationships in our data are statistically significant — that is, whether they are unlikely to have occurred by chance alone. Inferential statistics allow psychologists to make inferences about the population from sample data by testing hypotheses and calculating the probability that results are due to chance.

Key Definition: Inferential statistics are statistical tests used to determine whether the results of a study are statistically significant — that is, unlikely to have occurred by chance — and can therefore be generalised from the sample to the wider population.

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Probability and Significance

The Significance Level

In psychology, the conventional significance level is p ≤ 0.05 (5%). This means that the probability of the observed results being due to chance is less than or equal to 5% — or, equivalently, we can be at least 95% confident that the results reflect a real effect.