Reading for January 8

1. In paper 1(Correlation, regression and repeated data), how are the p-values in the table (and the third paragraph) computed?

2. In paper 3, example 1, the author says "The difference between the second mean for the subgroup and the population mean would be approximately r times the difference between the first mean and the population mean". Does "the second mean" here refers to the predicted mean through regressing the second measurement value on the first measurement value? According to paper 2, it is the predicted instead of the observed value of Y that is always fewer standard deviations from its mean than is X from its mean.

3. In paper 4, why the efficiency gains of ANCOVA compared with a change score are low when there is a high correlation between baseline and follow up measurements? How the efficiency gains are measured?