In a second step, an additional questionnaire was sent to centres that had reported procedure-related adverse events.
Questionnaires were administered to the participants before and after the visits and an additional questionnaire was administered to the attending cardiologist.
A second mailing with a reminder letter and an additional questionnaire were sent to those who had not responded three weeks after the initial mailing.
After two reminders by telephone including calling alternative numbers or sms, and after an additional questionnaire was mailed with no response, women were considered lost to follow-up.
Out of the responders to the 1961 questionnaire, a new questionnaire was sent to 21,863 eligible subjects in 1963 (response-rate 85.1 %), and in 1967 an additional questionnaire was sent to 20,576 eligible individuals (response rate 81.5 %).
In order to clarify and verify the initial findings, an additional questionnaire was sent to GOAL study participants in January 2008, which included questions asking for percentage use of shoe types during each decade of adulthood (Additional file 1).
For a sub-sample of 70 institutions, an additional questionnaire was used to obtain the actual costs of treating patients for all 59 conditions included in the Kenya Essential Package of Health (KEPH).
In the UK, an additional questionnaire was sent to the woman's GP about 18 months after delivery, and the date and cause of the death were provided by the Office for National Statistics.
In 2008, as part of the collection of blood samples in randomly selected participants in the Million Women Study, an additional questionnaire was sent to 14,762 women who had responded to the 2006 study questionnaire, and had not reported breast cancer or vascular disease.
An additional questionnaire was mailed to non-respondents and an additional week used to collect responses.
