Once R&D approval had been obtained, the Local Collaborator in each clinic was asked to identify and enumerate (but not name individually) the staff in their clinic who would be eligible for the questionnaire phase of the study.
Of those eligible for the questionnaire (n = 29 821 participants aged 16 59 years), 23 602 (79.1%) completed the module, 2297 (7.7%) refused and 3922 (13.2%) were unable to complete it without interviewer help (so they were not asked the domestic violence questions to maintain their safety).
239 (52%) questionnaires were eligible for analysis (if undeliverable questionnaires are disregarded response rate is 57%).
Eligible women were invited for questionnaire interviews, clinical examinations, and ultrasound measurements.
Of a total of 244,004 women eligible for the main questionnaires across the ten surveys, 94.9% participated.
We regarded the top 10 questions to be the most important questions in the questionnaire and the bottom 10 questions to be eligible for removal from the questionnaire.
Of these, 7,864 were eligible for the follow-up questionnaire in 2006, of which 6,307 responded (80%).
Eleven questions were eligible for removal from the questionnaire because they reduced the reliability of a scale, were not considered important by respondents, had high inter-item correlation, or a combination.
There is potential for non-participation bias, since nearly 20% (N = 6219) of those eligible for the self-completion questionnaire did not complete the domestic violence module, either because they refused (8%) or because they were unable to complete the module without interviewer help (13%).
Out of 2019 questionnaires eligible for the study, fifty five percent (1117) of the students were of Arab descent, and forty five percent (902) were Jewish.
