Questions regarding Dialysis study

Please supply three questions to clarify the choice of appropriate analysis

1. How is "sudden drop of blood pressure" defined?

2. Does the sequence of administration of dialysate at different temperatures have confounding effects? In other words, if a patient is assigned to the "cold" group, will (s)he be more/less likely to develop hypotension during the subsequent "hot" period compared with someone who is given warm dialysate at the beginning?

3. From the sample data it seems that all patients were monitored from late May to early August. Depending on the location of the study, the ambient temperature may change significantly during that period, and as such "room temperature" could be quite variable throughout the study if it is not kept more or less constant.

1. There are so many missing data here, which is likely to result in bias in estimation if just getting rid of them. So how can we deal with such a great deal of missing data?

2. In this case, is it necessary to consider clustering effect? How to estimate interclass correlation coefficient?

3. How to decide sample size here since no information about power and effetive size has been provided?

1. How is an episode of hypotension defined? Is there some threshold change in blood pressure that triggers an episode?

2. Are the investigators concerned with changes in blood pressure at different time points during dialysis? If not, is it appropriate to simply average blood pressure measurements taken through the course of one treatment?

3. Did the two groups receive the same number of cold and room temperature treatments?

1. Is it better to let one group merely receive warmed dialysate and the other merely receive room temperature dialysate?

2. Is the temperature of the warmed dialysate kept the same for each patient and in each time during the whole study period?

3. Should some other clinical(e.g kidney treatment history) and demographic information be considered?

1. How a sudden drop in blood pressure can be measured ?

2. The drop in blood pressure might possibly be due to a decrease in internal body temperature from where the Nephrologists hypothesized ? Is there any scientific evidence or statistical significance of their hypothesis ?

3. Why the blood pressure was recorded upto 4 hours ? Why not more than 4 hours ? Are the blood pressure measurements correlated ?

1) The "date" column in the data suggests that each subject underwent dialysis sessions on the same days (roughly speaking). Was this intentional such that we must incorporate the exact date into the analysis (compared with an analysis where order of trials didn't matter)?

2) within each session, do researchers expect (significant) time varying effect of dialysis on BP ?

3) since there are unequal numbers of hot/cold treatments per subject, does looking at the rate of incidence of hypo-tension the right measure to consider (which suggests some-kind of poisson regression)

1. What measure of blood pressure are you interested in? When talking about “drops” in blood pressure, we must be referring to one number.

2. Was blood pressure recorded strictly every hour, or were the recording times lenient?

3. Are you interested in the magnitude of the incidence of hypotension, or just the occurrence?

1. Were other potentially confounding variables also recorded for the patients (e.g. age, sex, etc.) and controlled for during the study? If not, can we check to see if there were significant differences between the groups in the study?

1. How rare is emphhypotension normally? If it is a rare occurrence, then we may, by chance, observe many instances of the adverse effect for one of the temperatures and mistakenly attribute the temperature as an indicator of emphhypotension.

1. Checking wikipedia, there seems to be 3 potential disadvantages to a cross-over study. (a) the order of the treatments may affect the results (b) there may be a "carry-over" effect of one treatment over to the next treatment and (c) a learning effect, which probably will not affect this study. How will issues (a) and (b) be addressed in the study?

1. Is the sudden drop of bleed pressure defined as number or percentage? Is it compared with the previous record or the baseline record? And should both systolic and diastolic blood pressure drop be taken into consideration?

2. If we want to explore whether temperature has any effect on blood pressure, should the normal fluctuation of blood pressure without dialysis for each subject also be recorded as control?

3. Are you interested in the episode or time if sudden drop happens? i.e. if hypotension exists for two subjects, but arrives at different times, are they treated the same or not?