USE OF A FOOD FREQUENCY QUESTIONNAIRE TO SCREEN FOR DIETARY ELIGIBILITY IN A RANDOMIZED CANCER PREVENTION PHASE-III TRIAL

Cancer prevention clinical trials use food frequency questionnaires (F FQs) to assist in eligibility screening, FFQ reliability and validity studies are available, but these studies do not evaluate FFQs as scree ning tools, The Wheat Bran Fiber Trial of the University of Arizona us ed a FFQ as an eligibility screen with the goal of screening out subje cts whose true daily calcium intake was less than 500 mg per day (for safety) and whose true dietary fiber intake was greater than 30 g per day (for safety and trial efficiency), Subjects ineligible by FFQ were interviewed for final dietary eligibility determinations, A study was undertaken within the Wheat Bran Fiber Trial to evaluate the sensitiv ity, specificity, positive predictive value, and negative predictive v alue (NPV) of the FFQ used in this context, Four-day food records were collected on 183 potential participants before entry into the study. Using the il-day averages as the ''true'' value, sensitivity, specific ity, positive predictive value, and NPV were calculated for men and wo men separately under two screening conditions: using the target calciu m and dietary fiber values and using ''revised'' values identified in interim analysis within the study. NPV was acceptable in all analyses, Sensitivity for low calcium intake was inadequate under the original criteria (0.33 for men and 0.09 for women) but acceptable under the re vised criteria (0.80 for men and 0.81 for women), With the revised cri teria, specificity declined, resulting in heavy screening burdens deem ed worthwhile for the safety considerations, Dietary fiber eligibility screening worked well at target values, These differences were not pr edicted by reliability/validity studies.