Feedback on Assignment 2

Part 1 - Initial Descriptive Analysis

As the investigators`s original question relates the occurrence of hypotension over the entire dialysis period, it makes most sense to include as much data as practical into the initial descriptive analysis.
Boxplots (or alternatives such as Violin plots) are very informative graphical methods. Since the distributions appear fairly symmetric, the mean and standard deviations are appropriate descriptive statistics. If the data is quite skewed, reporting medians and quartiles is preferred.

Reporting the occurrence of hypotension highlights a technical question. One can report the occurrence rates per dialysis session, or on a per person basis. The latter could be described by giving the number of patients experiencing any hypotension (by period and temp) or by describing patient using the proportion of sessions where hypotension occured (by period and temp).

Similarly, since the eventually analysis will be based on mean blood pressures for patients within period and temperature, it is also meaningful to create boxplots for these aggregate data points.

Whatever approach is taken, it is very important to specify exactly how the variables represented in plots and tables relate to the original data provided

Part 2 - Cross-over Analysis

In consideration of the formal analysis using the Hill`s Armitage approach, one should first provide summaries and plots of the change scores that will be used in the analysis.
As well the approach to calculate change scores (mean of differences or difference of means) needs to be specified. Most importantly, report of the analysis should emphasize inferences concerning the magnitude and direction of treatment and time effects by providing confidence intervals.

Part 3 - Analysis of covarance.

Nearly everybody answered this last question in a pragmatic way, by simply conducting an analysis of covariance. Once again, it is very important to describe the variables analysed in terms of the original data, and make it clear whether the analysis was on means or individual values from visits.

Additional points on presentation