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Table 1 Missing, temporary or duplicate unique identifiers (NHS number) by practice

From: Detecting referral and selection bias by the anonymous linkage of practice, hospital and clinic data using Secure and Private Record Linkage (SAPREL): case study from the evaluation of the Improved Access to Psychological Therapy (IAPT) service

Practice number List size Duplicate or default NHS number Missing NHS Number Total of NHS Number problems Missing Forename or Surname Missing Post-code Demographic data errors TOTAL
ERRORS
Errors as %
List size
  N n n n % n n n %
2 13552 0 145 145 1.07 2 26 173 1.28
14 7190 68 0 68 0.95 0 1 69 0.96
20 10354 61 0 61 0.59 0 0 61 0.59
15 5189 49 0 49 0.94 0 5 54 1.04
11 7611 52 0 52 0.68 0 0 52 0.68
13 11828 45 0 45 0.38 0 2 47 0.4
5 6875 6 1 7 0.1 0 38 45 0.65
19 4715 38 0 38 0.81 0 4 42 0.89
4 8951 36 0 36 0.4 0 0 36 0.4
12 5971 31 0 31 0.52 1 3 35 0.59
1 6661 2 0 2 0.03 0 28 30 0.45
17 7338 23 0 23 0.31 0 2 25 0.34
7 9508 0 14 14 0.15 0 10 24 0.25
6 7951 4 1 5 0.06 0 8 13 0.16
18 3740 11 0 11 0.29 0 2 13 0.35
9 4466 4 7 11 0.25 0 0 11 0.25
16 14708 6 0 6 0.04 0 0 6 0.04
3 10049 0 2 2 0.02 0 0 2 0.02
8 2092 0 0 0 0 0 0 0 0
10 3614 0 0 0 0 0 0 0 0
Total 152363 436 170 606 0.4 3 129 738 0.48