The 7-year follow-up questionnaire was administered in two ways - by internet as an ordinary paper version.  Letters were sent to participants' homes informing them of how they may access the questionnaire via the internet as well as informing them that they may request a mailed questionnaire to complete and return by ordinary mail using a prepaid envelope without having to access the internet questionnaire. If they did not respond to the first letter within a four week period, a second letter was sent as a reminder. If - at the end of a second four week period  - the internet version still had not been completed the paper questionnaire was sent automatically together with a prepaid envelope. No further letters to participants were sent, but completed forms were accepted and kept coming in for weeks and months after the third and last letter."