Table 2 Potential bias in the non-responders from the original sample and wave 2 interviews
From: Attrition and bias in the MRC cognitive function and ageing study: an epidemiological investigation
| Â | Cambridge | Gwynedd | Newcastle | Nottingham | Oxford | Total |
|---|---|---|---|---|---|---|
Refused wave 1 | 641 | 807 | 484 | 521 | 813 | 3266 |
   Traced | 641 | 806 | 482 | 518 | 808 | 3255 |
   Died | 123 (19) | 155 (19) | 115 (24) | 93 (18) | 177 (22) | 663 (20) |
Moved before wave 1 | 33 | 78 | 6 | 98 | 40 | 255 |
   Traced | 29 | 70 | 6 | 86 | 39 | 230 |
   Died | 10 (34) | 13 (19) | 1 (17) | 27 (31) | 11 (28) | 62 (27) |
Wave 1 interview complete | 2601 | 2625 | 2524 | 2514 | 2740 | 13004 |
   Traced | 2600 | 2622 | 2520 | 2510 | 2736 | 12988 |
   Died | 437 (17) | 384 (15) | 482 (19) | 409 (16) | 525 (19) | 2237 (17) |
Wave 2 status of those in wave 1 | Â | Â | Â | Â | Â | Â |
   Wave 2 interview complete | 1720 (66) | 1703 (65) | 1707 (68) | 1733 (69) | 1963 (72) | 8826 (68) |
   Died+ | 253 (10) | 238 (9) | 244 (10) | 277 (11) | 268 (10) | 1280 (10) |
   Died and Refused | 41 (2) | 56 (2) | 54 (2) | 31 (1) | 32 (1) | 214 (2) |
   Died and Moved | 0 (0) | 2 (<1) | 3 (<1) | 2 (<1) | 1 (<1) | 8 (<1) |
   Refused | 560 (22) | 590 (22) | 471 (19) | 431 (17) | 438 (16) | 2490 (19) |
   Moved | 27 (1) | 36 (1) | 45 (2) | 37 (1) | 36 (1) | 181 (1) |