What are the assumption(s) underlying this test? Do you think they are satisfied? (It is not necessary to perform a formal hypothesis test.)

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

1. Length of hospital stay

Table 3 of Zhang et al (2015) gives the analysis for length of hospital stay as

 a. What statistical test has been used?

b. Reproduce this result in SPSS (show the output).

c. What are the assumption(s) underlying this test?  Do you think they are satisfied?  (It is not necessary to perform a formal hypothesis test.)

d. Develop an appropriate linear model for evaluating whether there has been a treatment effect on length of hospital stay. You should only use demographic and baseline variables for prediction (i.e. do not use outcome variables to predict another outcome). Note that in order to evaluate whether there has been a treatment effect, treatment (Group) must be in the model, whether or not it is significant. Perform usual diagnostic model checking. Write down your final model.

e. In the clinical trials world, there is debate on whether treatment effects should be pre- sented as unadjusted or adjusted. Unadjusted treatment effects do not include any covari- ates besides treatment in the model, whereas adjusted treatment effects include baseline covariates that are found to be significant. Compute a similar regression model as in (d) for the unadjusted evaluation of treatment effect. (Just present the SPSS output.)

f. Does the PEP treatment have an effect on hospital stay? Compare your conclusions with that obtained by Zhang et al (2015), and discuss.

2. White cell count

White cell count has been measured at baseline (day 1) and as an outcome (day 5).

a. Is there evidence of baseline imbalance? (Examine graphical as well as numerical evi- dence.)

b. Develop an appropriate statistical model for determining the treatment effect on white cell count.

i. Perform diagnostic checking for your final model (examine residuals only);

ii. write down your final model;

iii. Is the treatment effective in reducing white cell count?

c. From Table 3, is there a treatment effect on White cell count on Day 5? Explain.

d. Comment on the difference between your method of analysis and that used by Zhang et al (2015) to arrive at the result given in Table 3.

 

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