StatisticsChapter 10Comparing two meansCategorical predictors in the linear modelIf we want to compare differences between the means of two groups, all we are doing is predicting an outcome based on membership of two groups.This is a linear model with one dichotomous predictor. Independent t-test: used when you want to compare two means that come from conditions consisting of different entities (this is sometimes called the independent-measures or independent-means t-test)Paired-samples t-test: also known as the dependent t-test. Is used when you want to compare two means that come from conditions consisting of the same or related entities.Rationale for the t-test Both t-tests have a similar rationale:two samples of data are collected and the sample means calculated. These might differ by either a little or a lotIf the samples come from the same population, then we expect their means to be roughly equal. Although it is possible for the means to differ because of sample variation, we would expect large differences between sample means to occur very infrequently. Under the null hypothesis we assume that the experimental manipulation has no effect on the participant’s behaviour: therefore, we expect means from two random samples to be very similar.We compare the difference between the sample means that we collected to the difference between the sample means that we would expect to obtain (in the long run) if there were no effect. We use the standard error as a gauge of the variability between sample means. If the standard error is small, then we expect most samples to have very similar means. When the standard error is large, large differences in sample means are more likely. If the...