What is included in the S4 specification for confidence intervals?
While working on the online resources for S4, we realised that some clarification of competence statement S4 I5 might be helpful. This covers confidence intervals for the difference between two population means in the unpaired situation. It should be read in conjunction with competence statement S4 I2 which covers the corresponding significance tests. Both the case of an interval based on the Normal distribution and the case of an interval based on the t distribution are included in S4 I5, as they are for the corresponding tests in S4 I2. The Normal case is, of course, for situations where the population variances are known or the samples are large. The t case is for situations where the samples are small and the population variances are unknown (but the populations are assumed Normally distributed. There is no specific reference to one-sided confidence intervals in the specification. These are touched on in the S4 textbook on page 129 but one-sided confidence intervals should be regar
