Basic Instructions

In the first article, what would be used when there are only two subjects with repeated pairs of observations on each ?

In the third article, the author states that for comparison of two methods of measurement the regression analysis has done with reported weight as the outcome variable and measured weight as the predictor variable. The slope of the regression was less than 1 in each study and the mean reported weighted of heavy subjects was less than their mean measured weight. The mean reported weight of light subjects was greater than their mean measured weight, how it comes ?

In the last article, the author states that the ANCOVA gains efficiency with a change score are low when there is a high correlation (say r > 0.8) between baseline and follow up measurements. What would the case when there is not a high correlation ?