11 year Follow-up

Code books and description of contact procedure

The 11-year follow-up questionnaires were available in a web-based version only. There were two questionnaires - one for the mother (father) and one for the child (the Club11 questionnaire). An updated version of both the parent and the Club11 questionnaires were launched on april 6th 2011. It was mainly a question of adding a few questions. The changes are reflected in the code books.

Invitation letter and 2 reminders

In both cases letters were sent to participants' homes informing them on how to access the questionnaire via the internet. If either mother or child did not respond within a four-week period, a second letter was sent as a reminder. This procedure was repeated four weeks later.

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.

11-year follow-up data documentation

Code book for adult - in Danish (pdf)

Code book for adult - in English (pdf)

Code book for child - in Danish (pdf)

Code Book for child - in English (pdf)

Screenshots from the child questionnaire - Club11 - in Danish (pdf)

Invitation letter and 2 reminders

Paper letters were sent to participants' homes informing them on how to access the questionnaire via the internet. If either mother or child did not respond within a four-week period, a second letter was sent as a reminder. This procedure was repeated four weeks later.

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.

Addresses and vital status updates every week

All information on participants in the DNBC was updated via the Danish Civil Registration System when the child turned 11 (once a week for the children who turned 11 that week). We mainly checked for change of address and vital status. If the child was registered as living with the father (in case of divorce or mother's death), the contact letters were sent to the father.

Letter versions

• The original invitation letters were ready for use on the 30th June 2010 and the reminder letters were drafted a couple of months later. On the 7th January 2011 new versions of theses letters were in place. Changes were mainly made to the section explaining how to access the website.
• On the  17th January 2011 we started to invite children who were already 12 years of age or older. The letters to this group had a slightly altered introduction.
• On the 7th April 2011 we changed the description concerning "difficult questions".
• In an attempt to make it more clear that the 11-year follow-up comprised two questionnaires (one for the mother and one for the child) further changes to the invitations letter were implemented  on the 18th April 2012.

Prizes

The drawing of monthly prizes was announced on the DNBC website on the 23rd March 2011 and on the back of the child letter on the 7th April 2011). Prizes were 4 cinema tickets per month and a gift voucher for DKK 5000,- every 6 months.