Retention of asthmatic patients in a longitudinal clinical trial

Prevention of study patient attrition and assessment of its impact on outcome data are problems that receive little attention despite their obvious importance in asthma research.

The medical, demographic, and psychologic characteristics of asthmatic children and adults who dropped out of a yearlong medication trial were assessed to determine whether this group differed from those who completed the study, potentially introducing bias into the data set and interfering with completion of the study's objectives.

Profiles of 362 adult and pediatric asthmatic patient dropouts from the multicenter trial were contrasted with profiles of those who completed the study. Despite a 1-month prerandomization screening, 24% of patients failed to complete the trial for varied reasons, which largely included noncompliance and treatment dissatisfaction.

Although attrition rates were equal among adults and children, dropout-completer differentiation was not. Adult completers did not differ from dropouts in any variables. However, pediatric dropouts were more likely than completers to be female (67% and 36%, p = 0.008) and to have more reactive airways (PD20, 2.29 +/- 1.32 and 5.2 +/- 1.23, p = 0.05), to have reduced scores on tests of intelligence (Full Scale IQ, 102.2 +/- 2.6 and 112.5 +/- 1.6, p = 0.002) and problem solving (Wisconsin Card Sorting Test Error Scores, 39.8 +/- 4.1 and 29.1 +/- 2.0, p = 0.01), and to have increased behavioral problems (Child Behavior Checklist Total Problem Score, 60.7 +/- 2.5 and 53.6 +/- 1.1, p = 0.003).

These findings demonstrate the potential of patient attrition to bias outcome in clinical trials and underscore the necessity of: (1) preventing its occurrence, (2) correctly assessing its causes, and (3) determining its ultimate impact on study results. Strategies for each of these three tasks should be implemented at the study's initial planning stages.