From: Attrition and bias in the MRC cognitive function and ageing study: an epidemiological investigation
 | Cambridge | Gwynedd | Newcastle | Nottingham | Oxford | Total |
---|---|---|---|---|---|---|
Ascertained | 3601 | 4654 | 3700 | 4100 | 4179 | 20234 |
   Died before sample date | 75 (2) | 32 (1) | 10 (<1) | 9 (<1) | 18 (<1) | 144 (1) |
   Moved before sample date | 24 (1) | 10 (<1) | 25 (1) | 33 (1) | 155 (4) | 247 (1) |
   Duplicates | 14 (<1) | 17 (<1) | 0 (0) | 6 (<1) | 6 (<1) | 43 (<1) |
   Wrong area | 0 (0) | 0 (0) | 196 (5) | 0 (0) | 18 (<1) | 214 (1) |
   DOB incorrect | 9 (<1) | 15 (<1) | 4 (<1) | 3 (<1) | 3 (<1) | 34 (<1) |
In scope | 3479 (97) | 4580 (98) | 3465 (94) | 4049 (99) | 3979 (95) | 19552 (97) |
   Language ineligible | 0 (0) | 16 (<1) | 3 (<1) | 27 (1) | 2 (<1) | 48 (<1) |
   GP refusal | 0 (0) | 24 (1) | 32 (1) | 69 (2) | 7 (<1) | 132 (1) |
   Relative | 0 (0) | 0 (0) | 1 (<1) | 0 (0) | 0 (0) | 1 (<1) |
   Never found | 14 (<1) | 75 (2) | 160 (5) | 70 (2) | 98 (2) | 417 (2) |
   Over sampled | 0 (0) | 752 (10) | 67 (2) | 565 (14) | 19 (<1) | 1403 (7) |
Available | 3465 (100) | 3713 (81) | 3202 (92) | 3318 (82) | 3853 (97) | 17551 (90) |
   Dead | 190 (5) | 203 (5) | 188 (6) | 185 (6) | 260 (7) | 1026 (6) |
   Refused | 641 (18) | 807 (22) | 484 (15) | 521 (16) | 813 (21) | 3266 (19) |
   Moved | 33 (1) | 78 (2) | 6 (<1) | 98 (3) | 40 (1) | 255 (1) |
   Screened | 2601 (75) | 2625 (71) | 2524 (79) | 2514 (76) | 2740 (71) | 13004 (74) |