Coherence is the degree to which data which have been derived from different sources or methods but refer to the same topic are similar. Comparability is the degree to which data can be compared over time and domain.
Obesity related hospital admissions
Changes to the figures over time need to be interpreted in the context of improvements in data quality and coverage, improvements in coverage of independent sector activity and changes in NHS practice.
Improved use of secondary diagnosis codes
There is continuing evidence that recording of secondary diagnosis codes is improving over time, which may have contributed (though not fully) to the increases seen in ‘admissions where obesity was a factor’ over the last ten years. This is demonstrated by looking at year on year increases in the mean number secondary diagnosis codes that were applied to these admissions as below.
| Year |
Mean diagnosis codes |
% Difference |
| 2007/08 |
4.5 |
1.8 |
| 2008/09 |
4.5 |
0.2 |
| 2009/10 |
4.6 |
2.0 |
| 2010/11 |
5.0 |
8.0 |
| 2011/12 |
4.9 |
-1.2 |
| 2012/13 |
5.0 |
1.7 |
| 2013/14 |
5.2 |
3.7 |
| 2014/15 |
5.3 |
1.9 |
| 2015/16 |
5.4 |
1.7 |
| 2016/17 |
5.6 |
4.0 |
| 2017/18 |
6.1 |
7.8 |
| 2018/19 |
6.5 |
7.0 |
Break in time series – 2019/10
There is a break in time series in 2009/10. Analysis of obesity coding of admissions data over time identified two issues affecting the obesity related admissions data prior to 2009/10. Firstly, in 2009/10 the introduction of a specific procedure code for maintenance of gastric band added approximately 1,500 records in that year. Secondly, there is evidence that the obesity primary diagnosis code was not applied as consistently before this time, based on analysis of the proportion of bariatric surgery records that included an obesity primary diagnosis.
This effects all the admissions time series data but most significantly ‘admissions attributable to obesity’ (tables 2.1 and 2.2) and ‘obesity admissions for bariatric surgery‘ (tables 4.1 and 4.2). It is less significant in the ‘admissions where obesity was a factor’ measure (tables 3.1 and 3.2), as the impact represents a much smaller part of that data.
Changes to recording of gastric band maintenance
Practices vary between hospitals as to whether gastric band maintenance procedures (introduced as a specific OPCS-4.5 code from 2009/10) are recorded as being carried out in outpatient or inpatient settings. As the data presented in this report are for inpatients only, inconsistencies over time have contributed to the changes seen in recent years. Time series data that excludes maintenance and revisional procedures, (thus removing the effect of these varying recording practices) is shown in table 4.1 (Primary bariatric surgery).
Most providers record none or very few gastric band maintenance procedures as inpatient admissions, but the changes known to us that have a significant effect on the national totals are as below. Though this affects all the obesity related admissions measures (with the exception of primary bariatric surgery), it is less significant in the ‘admissions where obesity was a factor’ measure (tables 3.1 and 3.2), as bariatric surgery represents a much smaller part of that data (less than 1% in 2017/18).
Please note, the figures quoted are for episodes involving gastric band maintenance where there was no primary bariatric surgery in the same episode (as those that also had a primary bariatric surgery procedure code would be included in the counts regardless).
2013/14
Between 2009/10 and 2012/13 Derby Hospitals NHS Foundation Trust (RTG) recorded around 750 to 1,250 obesity related admissions per year involving gastric band maintenance. In 2013/14 and subsequent years this number was zero or close to zero. In 2013/14 this change represented around half of the decrease in the national bariatric surgery figures (-1,640 overall).
Between 2009/10 and 2012/13 King’s College Hospital NHS Foundation Trust (RJZ) recorded around 250 to 400 obesity related admissions per year involving gastric band maintenance. In 2013/14 this number dropped to 53, and just 2 in 2014/15. They have since recorded around 100 per year.
2015/16
From 2015/16 Heart of England NHS Foundation Trust (RR1) has recorded around 300 to 400 obesity related admissions per year involving gastric band maintenance, compared to close to zero prior to 2015/16. In 2015/16 this change accounted for around three quarters of the increase in the national bariatric surgery figures (+406 overall).
Changes to procedure codes effecting the bariatric surgery time series
In 2012/13, changes were made to give a standard definition of “bariatric surgery” using the same methodology as Healthcare Resource Groups (HRGs). The new HRGs were created in 2011/12 Reference Costs collection as a result of work between the National Casemix Office at NHS Digital, the British Obesity and Metabolic Surgery Society (BOMSS) and the Chapter F Digestive System Expert Working Group (EWG). This definitional change has a minimal effect on the previous years’ data; between 20 and 30 cases a year from 2009/10 onwards when OPCS 4.5 and 4.6 codes were used, following on from the introduction of a specific code for maintenance of gastric band in OPCS-4.5 in 2009/10. Appendix B shows the current list of OPCS codes included in the definition of bariatric surgery.
More information on the change of codes in 2012/13 is included in the methodological change notice.
In 2016/17, the National Casemix office updated the definition above to remove 2 previously included OPCS codes, and so the data in this publication has been updated to reflect this, creating a break in time series from 2016/17. Based on data in recent years (2015/16 to 2017/18), the change reduces the total by between 250 and 320 records per year.
More information on the change of codes in 2016/17 is included in the methodological change notice.
Changes to the calculation of hospital admission rates
Admission rates per head of population were changed in the 2017 report to be age standardised based on the European Standard Population. Prior to 2017, these rates were not standardised. More information is available from the methodological change notice.
Other HES data issues
2016/17
Around one third of all records for Nottingham University Hospitals Trust were submitted to the Hospital Episode Statistics database without patient identifiers such as postcode. This means it was not possible to assign a Local Authority or Clinical Commissioning Group of Residence to these admission records, so they will not appear in the tables. This will mainly affect the Nottingham and Nottinghamshire areas with a smaller impact on surrounding areas and the East Midlands and England totals.
