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An Assessment of the NIH Women's Health Initiative
most of which were then included in the CT questionnaires. * The variables remaining in the supplemental questionnaire, which will be given only to OS participants, reflect more speculative issues than those addressed by the CT. However, although the WHI Manual ofOperations and Procedures notes that “(t)he content of the supplemental questionnaire is directed to the epidemiology of primary outcomes that are relatively common, serious, and capable of being readily ascertained by means of the planned OS follow-up mechanisms” (1993), the committee was provided with little information about the possible specific etiologic associations and the additional hypotheses being studied in the OS.
DESIGN AND METHODS
The OS is designed as an observational prospective cohort study. Women who have been contacted and expressed interest in the CT, but who are ineligible or unwilling to participate, will be asked to participate in the OS. Being drawn from the same area and age group, the women in the OS and CT will be in some ways comparable and, as volunteers, are likely to be different from the population as a whole. The women in the OS are likely to differ from CT participants in other respects, including their health behavior, history, and status. The incidence rates of disease and the extent of exposure to risk factors may be different among the CT, OS, and the general populations.
Despite, the OS participants having been drawn from a “convenience” sample, not a population-based sample, the OS population will be useful for examining associations between possible risk factors and disease; there is no a priori reason to believe that associations between possible risk factors and diseases will be different in this subgroup.
In addition to the information obtained by questionnaires, a fasting blood draw (and in some cases a urine collection) will provide specimens to be frozen and stored. The May 1991 Repository Feasibility Study from the National Cancer Institute estimates that between 10 and 20 million samples will be stored for the entire CT and OS populations. Serum storage is potentially valuable because it is likely that over the next several years hypotheses concerned with biological markers of exposures or of early disease will be formulated outside of the WHI that can be examined in this study population. A 1 percent subsample stratified on age, racial/ethnic group, and socioeconomic status will have repeat baseline information after the first screening visit so that the reliability of the data can be determined and error correction methods applied. This reliability testing strengthens the study.
Questionnaire categories include: Personal Information, Medical History, Reproductive History, Family History, Personal Habits, Psychosocial, Food Frequency, and OS Supplement.