Time | Questionnaire | Exposure measurement | Outcome measurement |
---|---|---|---|
May 1998 (baseline) | Extensive | • | • |
September 1998 | Short | • | |
January 1999 | Short | • | |
May 1999 | Extensive | • | • |
September 1999 | Short | • | |
January 2000 | Short | • | |
May 2000 | Extensive | • | • |
September 2000 | Short | • | |
January 2001 | Short | • |