Reading for January 8

1. (Paper 1) The method of finding the correlation between means should allow us to compute shorter confidence interval for the correlation coefficient (since the mean for a group is based on a number of observations in that group and is different from having only one observation that happens to have the value at the mean). How should we incorporate the number of observations in each group in such calculation?

2. (Paper 3) The sentence "Even if subjects are not treated the mean blood pressure will go down" is quite confusing. Sure enough BP can increase, thus bringing up the mean. Judging from the second paper it seems that those comparisons are made in terms of number of standard deviations, but still they pertain to the fitted/estimated slope only, not the observed ones.

3. (Last paper) The multiple regression / ANCOVA method uses only the main effects (baseline score and group). I wonder what interpretations can we develop by adding an interaction term - certainly the estimates of a and b will be different compared with those obtained in the main effects model.