Data
Hospital Episode Statistics (HES) for hospital admissions in England for the 11-year period 2002/03 to 2013/14 (financial year 1st April to 31st March) were supplied by NHS Digital. HES data are routinely collected administrative data that record any hospital activity. Information extracted included the personal characteristics of each patient (age, sex, location of residence), along with up to 20 diagnoses. Data comprised individual ‘episodes’, each of which is a continuous period of care under a single consultant doctor during an admission.
We followed the approach taken by Public Health England, an executive agency of the Department of Health responsible for health promotion and protection, for identifying alcohol-related admissions [
25]. Firstly, the data set was cleaned to address some known issues with HES. Only episodes that were finished, and were ‘ordinary’ (non-elective admissions or an elective admission expected to remain in hospital overnight), day case (elective admissions not requiring an overnight stay) or maternity admissions were included. We removed admissions with an age at the beginning of admission outside the range of 0 to 120, or where the sex was not recorded as male or female. We only considered admissions with an English postcode of residence so that our national estimates remained consistent with our estimates by level of deprivation, since the deprivation data were assigned using a patient’s residential address. This produced a small undercount of estimates as some admissions with unknown address or no fixed abode were alcohol-related (see Note 7 in Additional file
1: Table S1), but was necessary to allow for consistency in the data used throughout our results. The percentage of episodes which remained following cleaning over the study period was 89.72% (see Additional file
1: Table S1 for more details).
Alcohol-related conditions were weighted using Public Health England’s age group and sex specific population attributable fractions (PAFs) [
25,
26]. PAFs represent the proportion of cases (i.e. hospital admissions) at the population level that might be attributed to an exposure (i.e. alcohol consumption). PAFs were age- and sex-specific, and were adjusted for alcohol consumption [
26]. Negative PAFs, which suggest a protective effect of alcohol, were excluded. We identified alcohol-related admissions based on Public Health England’s ‘narrow’ measure. Our approach is defined in the paragraph below.
Each HES episode can contain up to 20 diagnoses, with the first diagnosis being the primary diagnosis (diagnoses were coded using ICD-10 throughout the study period). The narrow measure was calculated based on the primary diagnosis of an admission, with external conditions taken from secondary diagnostic positions 2 to 14 (external conditions, which are environmental causes of injury occurring outside the body, do not feature as the primary diagnosis). During the time period studied, the number of secondary diagnostic positions was expanded from 14 to 20, but we only considered up to 14 so that there was consistency throughout the period. Where there were multiple alcohol-related conditions recorded within an episode, we classified the admission using the condition with the largest PAF. If there were two conditions with the same PAF, we used the one from the lowest diagnostic position (i.e. closest to diagnosis position 1). An admission can comprise more than one episode of care if patients are transferred from the care of one consultant to another. However, 86.7% of all episodes only contained a single episode. We considered only the first episode from each admission.
We used four outcome measure categories of alcohol-related harm based on previous research [
25‐
27]. These were (i) acute conditions wholly attributable to alcohol consumption, (ii) chronic conditions wholly attributable to alcohol consumption, (iii) acute conditions partially attributable to alcohol consumption, and (iv) chronic conditions partially attributable to alcohol consumption. Additional file
2: Table S2 presents which conditions were found in each category (based on Public Health England’s guidance). For acute conditions, we considered only emergency admissions. For chronic conditions, we combined emergency and non-emergency admissions.
In addition, we also examined four specific conditions which were wholly attributable to alcohol consumption, two acute and two chronic. These were the most common specific conditions within the acute and chronic wholly attributable to alcohol categories. The two acute conditions were (i) ‘Acute Intoxication subcategory of Mental and Behavioural Disorders due to use of Alcohol’ (ICD-10 code F10.0), and (ii) ‘Intentional self-poisoning due to alcohol’ (ICD-10 code X65). The two chronic conditions were (i) ‘All other Mental and Behavioural Disorders due to use of Alcohol’ (ICD-10 code F10.1-F10.9), and ‘Alcoholic Liver Disease’ (ICD-10 code K70).
We also calculated ‘non-alcohol’ related admissions to understand how our other measures compared to general trends in admissions. Non-alcohol related admissions were identified as any admission that contained a condition that had no known association to alcohol as defined using the population attributable fractions used previously (i.e. PAF = 0). We chose to exclude any condition with a partial association.
Counts of admissions were calculated for each outcome measure by Lower Super Output Area (LSOA). LSOAs are census areas created to disseminate administrative data and contain an average population size of approximately 1500 people. This allowed analysis by area-based socioeconomic deprivation. Annual mid-year Office for National Statistics (ONS) population estimates for LSOAs by five year age band and sex were used to calculate rates. We also attached the English Indices of Deprivation (IMD). IMD is a multi-dimensional neighbourhood-level indicator of socioeconomic deprivation for LSOAs [
28]. We used the ‘income deprivation’ domain to avoid circularity issues since the overall index contains a health domain. Each measure of IMD was divided into categories based on quintiles of its level of income deprivation. IMD scores were assigned to HES records based on the closest year for which IMD scores were available (2004, 2007, and 2010). The 2015 index was not available at the time of analysis.