= 2673
D)
n
= 3680

5. A clinical trial is being conducted in order to determine the efficacy of a new drug that will be
used to treat rheumatoid arthritis. The efficacy of the medication will not only be determined by
the physical improvement of symptoms but will also be determined by using a blood test to
examine the concentration of C-reactive protein (an inflammatory marker) in an individual’s
blood. If the researcher wants a margin of error for the level of C-reactive protein to be less than
or equal to 1.5 mg/d and if the standard deviation for C-reactive protein concentrations among
arthritis patients was previously documented at 6 mg/dL, how many patients should be recruited
for each group of individuals in the study, assuming a 95% confidence interval will be used to
quantify the mean differences between the control group and the treatment group?

1. True or False? To calculate the finalized n for a study, one should take the total number of
participants needed to ensure the desired confidence interval and divide it by the proportion of
individuals expected to be retained throughout the course of the study.
2. True or False? A researcher wants to be sure the mean difference in the change in blood
pressure has a margin of error no more than 5 points and the difference in the standard deviation
between the mean blood pressure points from the first medication used to treat high blood
pressure and the second medication used to treat high blood pressure is 14 points. The desired
sample size required to ensure a 95% confidence interval for the proposed study used to compare
the efficacy of two medications used to treat high blood pressure during a cross-over trial is
n
31.
=