1. ARandomizedClinicalTrialwasdesignedtocomparetheeffectivenessof twodifferentantiretroviral(ARV)drugsinpatientsco-infectedwithTBandHIVin Korea.Asamplesizeof660pergroupwaschosentohave90%powertodetectadifferenceinmeanCD4at1yearof25basedonanestimatedstandarddeviationof140.

A. Whichofthefollowingisanaccurateinterpretationofthe90%powerofthisstudy? (circle1)

1. We will have a 90% chance of finding a significant difference if the observed mean of the two treatment groups differs by 25 and the standard deviation is 140.

2. There is a 90% chance that the observed difference will be 25 or more if the standard deviation is 140.

3. At the end of the study, if the standard deviation is 140 then on average 90% of the data will be contained in a 90% confidence interval.

4. We will have a 90% chance of finding a significant difference if the true mean of the two groups differs by 25 and the standard deviation is 140.

B. If thetruestandarddeviationinthispopulationis210,willthestudyhave moreorlesspowerthan expected?

C. Allparticipantswillbeobservedforexactlyoneyear,atwhichpointtheirCD4count ismeasured.Oncethestudyisover,whattypeoftestcanbeusedtocomparethe observeddifferencesinCD4countbetweenthetwogroups?

D. Theinvestigatorsareconsideringaddingathirdandfourthgroupwhowouldreceive twootherARVs.Iftheydoso, whattestwouldyouuseto simultaneously compare the four ARVs with respect toCD4?

E. What is the problem with comparing all pairs of ARVs using a t-test at alpha=0.05 for each?