PSEUDO_HESID

In order to identify episodes that relate to a single patient, a PSEUDO_HESID value is assigned to every episode.

If the patient identifying information recorded on two episodes is thought to belong to the same patient, the same PSEUDO_HESID is assigned to both.

Therefore, the PSEUDO_HESID is effectively a HES patient identifier.

Patient PSEUDO_HESID Index

A Patient PSEUDO_HESID Index is used to record the PSEUDO_HESIDs that have been assigned to combinations of the data items involved in the matching steps outlined below.

There is only one Patient PSEUDO_HESID Index, which is independent of the data years, to facilitate linking of episodes across data years.

Linking/matching process

In outline, the matching process involves three main steps:

1. The first step attempts to match episodes using the following patient identifying information:
• SEX (Sex)
• DOB (Date of Birth)
• NEWNHSNO (NHS Number)
2. The second step then attempts to match episodes using:
• SEX (Sex)
• DOB (Date of Birth)
• HOMEADD (Postcode)
• PROCODET + LOPATID (Local Patient Identifier within Provider)
3. The third step then attempts to match episodes using:
• SEX (Sex)
• DOB (Date of Birth)
• HOMEADD (Postcode)

Linking rules

As a general rule, matching is attempted only if all of the values required by that step are non null and valid.

• A DOB is valid if:
  • It is not null;
  • It is a valid date;
  • It is no earlier than 1895/01/01;
  • It is not later than the end of the current data year.
• An NHS Number is valid if:
  • It is not null;
  • It consists of exactly 10 digits;
  • The 10 digits are not all the same;
  • The check digit is correct.
• A Postcode is valid if:
  • It is not null;
  • It is exactly 8 characters long;
  • It is of the format AXXX 9AA, AXX 9AA, or AX 9AA, where A is any uppercase alphabetic character (A - Z), X is any uppercase alphanumeric character (A - Z, 0 9), 9 is any digit (0 9), and is a space;
  • It does not start with 'ZZ'.
• For matching purposes, all spaces and zeros are removed from Local Patient Identifiers.
• Two DOBs match if:
• A Postcode is valid if:
• Neither DOB is 1901/01/01;
• Neither DOB is 1899/12/31;
• The two DOB values are no more than 14 years apart;
• The two DOB values are the same; or two components (ie YYYY, MM, DD) of the two DOB values match; or two components of the two DOB values match when the MM and DD parts of one of them are swapped.