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

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)