Objectives: This paper presents the results of a pilot study of job-specific modules developed for use in the study questionnaire of the Northern California Childhood Leukemia Study (i) to estimate the variability in response between people administered the same module and (ii) to estimate the number of modules required per family.
Methods: For 63 participants in the pilot study, between-person variability was assessed by comparing reported job tasks among the respondents administered the same job-specific module. Within-respondent variability was assessed by examining changes in the timing and frequency of the job tasks and product use across critical time segments from 12 months before the child's birth to 3 years of age. Parental occupational histories were reviewed to estimate the expected number of job-specific modules required per family.
Results: Considerable variability was identified for the tasks performed by the respondents with similar jobs and in the timing of tasks and products used across critical time windows. Parents' occupational histories indicated that detailed exposure information could be obtained for 95% of the families with a maximum of two job-specific modules added to the study interview.
Conclusions: The job-specific modules captured individualized exposure information for the parents of cases and controls and thus reduced the potential for nondifferential misclassification when compared with the use of a job title approach, while avoiding an exposure checklist approach. These improvements in exposure estimation may increase the statistical power for identifying any true association between parental occupational exposures and childhood leukemia.