Which of the following statements are true?

Note that there may be more than one correct answer; select all that are true.

If the two populations are not normally distributed , then the inference procedures for the difference between two means can still be valid , provided the sample sizes are large. The sampling distribution of* - *, is approximately normal , provided the independent sampling distributions of * , and * , are themselves approximately normal . The results obtained from the pooled - variance I procedure Versus the Welch procedure , when applied to the same data set , will always be significantly different . One problem with taking observations on the same experimental unit , as in a paired difference test , is that it can increase the variability in the experiment . The paired difference procedure is less susceptible to the populations being non - normal , since taking the difference* between two non - normal populations will result in a normal distribution