Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Figure 9. A scatter plot showing the relationship between CD4 cell counts at baseline and at week 48in the MaxCmin 1study (n = 272).1,2001,000CD4 count at week 48 (cells/mm 3 )80060040020000 200 400 600 800 1,0001,200Baseline CD4 count (cells/mm 3 )––––– fitted values.Line graphs can be used to depict fluctuating data containing peaks and troughsand are good for identifying trends. They are also used to show how the mean ormedian measurement of a marker fluctuates over time by treatment group.Figure 10 shows the mean systolic blood pressure (SBP) at seven different timepoints for 2,028 patients followed over 36 months in an anonymous study. Thedots correspond to the mean SBP at each visit and error bars have been added toshow ± one standard error. This graph shows that SBP was consistently lower ingroup A compared to group B after randomization.Kaplan–Meier plots are a type of line graph that are used to show how thepercentage of patients who are event-free changes over time (see Chapter 21).Another example of a line plot is the receiver operating characteristic curve,which is a plot of the true-positive rate (sensitivity) versus the true-negative rate(1 – specificity) of a diagnostic test.419