Past exam of the experimental design and methods course of the year 2 of the psychology (experimental) course of the University of Oxford / 2022 / 3 / c

Use a Student t-test to assess a mean or mean difference relative to its standard error. A one-sample version compares a population mean with a specified reference. An independent two-sample version compares two separate groups, such as groups assigned different instructions; Welch's t-test permits unequal group variances. A paired t-test uses within-pair differences, such as each participant's before/after scores, rather than pretending those measurements are independent.^[ref]

The relevant normality assumption concerns within-group errors for the independent-groups model or the distribution of within-pair differences for the paired model. Independent participants or pairs remain essential. Report the estimated difference and its confidence interval together with the test result. A small p-value indicates incompatibility with the specified null hypothesis under the model; it does not measure the size of the difference, the probability that the null hypothesis is true, or whether the difference matters practically.