Variations in outcome measures with different sampling frequencies
| Sample weekly | Sample weekly exclude week 1 | Sample every 2 weeks* | Sample every 4 weeks† | |
|---|---|---|---|---|
| Number of completed questionnaires | 3848 | 3538 | 1774 | 896 |
| Number of problems | 419 | 361 | 318 | 280 |
| Number of substantial problems | 142 | 124 | 94 | 72 |
| Average prevalence (all problems) | 39 (34–44) | 37 (34–41) | 39 (34–44) | 40 (31–50) |
| Average prevalence (substantial) | 13 (12–15) | 12 (11–14) | 13 (10–15) | 13 (9–17) |
| Average severity score | 28 (27–29) | 28 (27–29) | 28 (26–29) | 27 (26–27) |
| Average duration of problems (weeks) | 5 (4–5) | 5 (4–5) | 3 (1–4) | 2 (1–2) |
*Weeks 2, 4, 6, 8, 10 and 12
† Weeks 2, 6 and 10.