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Table 1 Assessing the accuracy of NHS numbers in routine data.

From: The SAIL databank: linking multiple health and social care datasets

Data Source Type of Record Linkage Result of comparing the NHS number allocated by the record linkage process with the original submitted NHS number
   Same Different Not found % Agreement % Disagreement % Linked
   Allocated NHS number equals the submitted NHS number Allocated NHS number differs to the submitted NHS number An NHS number is not found by the record linkage process Of the records that were allocated an NHS number, the percentage that were allocated an NHS number equal to the NHS number submitted Of the records that were allocated an NHS number, the percentage that were allocated an NHS number different to the NHS number submitted Of the records that were processed, the percentage that were allocated an NHS Number
   a b c = a/(a+b) = b/(a+b) = (a+b)/(a+b+c)
Primary Care Practice Clinical Systems (GP) (n = 229,117) DRL 223,344 40 5,733 99.982% 0.018% 97.498%
  PRL – 99% cut off 227,778 51 1,288 99.978% 0.022% 99.438%
  PRL – 95% cut off 228,288 55 774 99.976% 0.024% 99.662%
  PRL – 90% cut off 228,479 56 582 99.976% 0.025% 99.746%
  PRL – 50% cut off 228,699 61 357 99.973% 0.027% 99.844%
Secondary Care Hospital Admissions (PEDW) (n = 264,868) DRL 216,062 323 48,483 99.851% 0.149% 81.695%
  PRL – 99% cut off 244,692 410 19,766 99.833% 0.167% 92.537%
  PRL – 95% cut off 247,865 439 16,564 99.823% 0.177% 93.746%
  PRL – 90% cut off 249,024 453 15,391 99.818% 0.182% 94.189%
  PRL – 50% cut off 250,155 465 14,248 99.815% 0.186% 94.621%
  1. This shows the level of agreement between NHS numbers supplied in the General Practice (GP) dataset (n = 229,117) and the Patient Episode Database for Wales (PEDW) dataset (n = 264,868) with those allocated by the matching process using by DRL and PRL. The NHS Administrative Register (NHSAR) was used as the reference.