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Data set, Part of

SHMI primary diagnosis coding contextual indicators

Date Range:
01 Sep 2020 to 31 Aug 2021
Publication Date:
Next Publication Date:
10 Feb 2022
Geographic Coverage:
Geographical Granularity:
NHS Trusts


These indicators are designed to accompany the SHMI publication.

Information on the main condition the patient is in hospital for (the primary diagnosis) is used to calculate the expected number of deaths used in the calculation of the SHMI. A high percentage of records with an invalid primary diagnosis may indicate a data quality problem. A high percentage of records with a primary diagnosis which is a symptom or sign may indicate problems with data quality or timely diagnosis of patients, but may also reflect the case-mix of patients or the service model of the trust (e.g. a high level of admissions to acute admissions wards for assessment and stabilisation).

Contextual indicators on the percentage of provider spells with an invalid primary diagnosis and the percentage of provider spells with a primary diagnosis which is a symptom or sign are produced to support the interpretation of the SHMI.


1. As of the July 2020 publication, COVID-19 activity has been excluded from the SHMI. The SHMI is not designed for this type of pandemic activity and the statistical modelling used to calculate the SHMI may not be as robust if such activity were included. Activity that is being coded as COVID-19, and therefore excluded, is monitored in the contextual indicator 'Percentage of provider spells with COVID-19 coding' which is part of this publication.

2. Please note that there has been a fall in the overall number of spells due to COVID-19 impacting on activity from March 2020 onwards and this appears to be an accurate reflection of hospital activity rather than a case of missing data. Further information is available in the contextual indicator ‘Provider spells compared to the pre-pandemic period’ which is part of this publication.

3. On 1 October 2021 Pennine Acute Hospitals NHS Trust (trust code RW6) merged with Salford Royal NHS Foundation Trust (trust code RM3). The new trust is called Northern Care Alliance NHS Foundation Trust (trust code RM3). This new organisation structure is reflected from this publication onwards.

4. A previous issue where Mid and South Essex NHS Foundation Trust (trust code RAJ) had missing or incorrect information for the patients’ primary diagnosis has now been corrected in the underlying data. This trust is now included in the SHMI again from this publication onwards.

5. Day cases and regular day attenders are excluded from the SHMI. However, some day cases for University College London Hospitals NHS Foundation Trust (trust code RRV) have been incorrectly classified as ordinary admissions meaning that they have been included in the SHMI. Maidstone and Tunbridge Wells NHS Trust (trust code RWF) has submitted a number of records with a patient classification of ‘day case’ or ‘regular day attender’ and an intended management value of ‘patient to stay in hospital for at least one night’. This mismatch has resulted in the patient classification being updated to ‘ordinary admission’ by the Hospital Episode Statistics (HES) data cleaning rules. This may have resulted in the number of ordinary admissions being overstated. The trust has been contacted to clarify what the correct patient classification is for these records. Values for these trusts should therefore be interpreted with caution.

6. Further information on data quality can be found in the SHMI background quality report, which can be downloaded from the 'Resources' section of the publication page.