The results of the pilot questionnaire were used to develop the main study questionnaire.
The response rate to the main study questionnaire was 60% (2504/4171) of whom 41% had chronic pain and 1979 of whom were included in the multi-variate analysis.
The regression intercepts and slopes that were obtained from the calibration study were then applied to the main study questionnaire data to obtain individual predicted values of dietary exposure for all participants.
Data collection was conducted during an in-person interview, which included the administration of a main study questionnaire querying about demographics, family history, reproductive history, hormone use, lifetime alcohol consumption, physical activity and other lifestyle factors.
Because exposure status at the time of blood draw might be most strongly correlated with estradiol, we also evaluated each of the variables at the time of blood draw or, for variables ascertained only on the main study questionnaire (for example, alcohol intake), within 2 years of blood draw.
Before the main study, the questionnaire was tested on a sample of parents.
The study proceeded in two parts: in the main study a questionnaire was mailed to a random sample of 600 GPs drawn from the Danish Medical Association's department of registration.
To correct for centre-specific bias and regression dilution within each centre stratum, the 24-HDR values for participants of the calibration study were regressed on their main study dietary questionnaire values, providing regression coefficients for fish consumption.
The primary outcome of product acceptability was examined separately for the diaphragm and for the gel using a variable from the MIRA main study acceptability questionnaire administered at the study's closing visit: "How would you rate the [diaphragm/gel] overall?": "strongly like, like, dislike, strongly dislike".
Following completion of the main study follow up questionnaires 12 months after entering the trial, potential participants were invited to discuss their experiences of treatment over the past year.
