The design incorporated a secondary analysis of Hospital Episode Statistics (HES) and the most contemporaneous Index of Multiple Deprivation (IMD) 2007 and Local Index of Child Well-being (CWI) 2009.
HES is a national data warehouse containing details of admissions to National Health Service (NHS) hospitals in England and NHS commissioned activity in the independent healthcare sector. HES data are recorded as Finished Consultant Episodes (FCEs) which represent a period of admitted patient care under a consultant within an NHS Trust. FCEs are not analogous to a single stay (spell) in hospital because a patient may transfer between two consultants during their stay. FCEs (n = 23,955) were therefore linked to create spells (n = 23,496) prior to analysis. Most spells (n = 23,062, 98.1%) comprised a single FCE and a small number (n = 434, 1.9%) included more than one FCE. There were 72 inter-hospital transfers.
HES were obtained for all children aged 0-14 resident in one of 10 adjacent PCTs serving a metropolitan area in North West England discharged during the 2006/07 financial year following emergency admission to NHS hospitals in England. The upper age limit of 15 years was determined by the age bands in which population data are published by the Office for National Statistics (ONS).
Analysis was conducted as part of a larger research project that assessed the costs and effects of different models of Community Children's Nursing Teams (CCNT) that provide alternative care to hospital admission during acute illness [12
]. Emergency admissions for the three commonest medical presentations at paediatric EDs (i.e., breathing difficulty, feverish illness and diarrhoea [5
]) were selected for analysis in consultation with local paediatricians as these conditions may be managed at home by CCNTs. Although breathing difficulty, feverish illness and diarrhoea combined account for around half of medical ED attendances [7
] these three categories do not however capture the full range of childhood acute illness. International Classification of Disease (Revision 10) (ICD-10) diagnosis codes used to derive these three categories of admission are shown in (Additional file 1
: Table S1).
The three categories of admission are not reported separately because children could be diagnosed with a combination of breathing difficulty, feverish illness, and diarrhoea during a single admission. Most admissions (n = 19,376, 82.5%) were classified into only one of the three condition categories (breathing difficulty: n = 11,780, 50.1%; feverish illness: n = 4,473, 19.0%; diarrhoea: n = 3,123, 13.3%). Around one in every six admissions (n = 4,030, 17.1%) included diagnoses which were classified into two condition categories (breathing difficulty and feverish illness: n = 3,361, 14.3%; breathing difficulty and diarrhoea: n = 341, 1.5%; feverish illness and diarrhoea: n = 328, 1.4%). Ninety (0.4%) admissions included diagnoses classified into all three condition categories.
There is a risk of errors persisting even after processing prior to publication of HES data, and these are known to be more frequent in more specific diagnosis codes and to vary between geographical regions (North West England has one of the lowest error rates) [14
]. Clinical coding practice may also differ across hospitals. The potential impact of coding error and disparity was minimised by: (1) selecting conditions predominantly at the 'block' level of the ICD-10 coding structure rather than specific diagnostic codes; (2) identifying emergency admissions in each condition category by examining all fourteen available diagnosis fields in HES rather than reliance on the primary diagnosis because symptoms rather than diagnoses may be recorded in this field following initial assessment; (3) aggregating the three condition categories prior to analysis due to co-morbidity.
EARs were calculated as the number of in-patient spells per 1,000 children aged 0-14 resident in each PCT. As HES do not record admission and discharge time it is possible for an overnight stay (with a recorded length of stay of 1 day) to be shorter than a same day discharge (0 day). EARs were therefore disaggregated by length of stay in three groups: 0 or 1 day; 2 or 3 days; 4 or more days. Age groups were constructed to match those reported by ONS mid-2006 population estimates which were used as the denominator: under 1 year; 1-4 years; 5-9 years; 10-14 years. PCTs were selected as the unit of analysis as the contemporary level at which NHS care was commissioned.
The primary measure of deprivation was the published average IMD 2007 score for each PCT obtained from the Department of Communities and Local Government [15
Secondary measures of childhood disadvantage were selected domains of the CWI 2009 [16
]. The CWI 2009 includes seven domains combined with equal weights: material, health, education, crime, housing, environment, and children (at risk of being) in need.
Indicators used to derive the material domain included the percentage of children under 16 years old that live in families reliant on means-tested benefits including: Income Support, Income-Based Job Seekers Allowance, Working Tax or Child Tax Credit. The health domain included rates of emergency admission and outpatient attendance for children aged 0-18 years old and the percentage of children aged 0-16 years old in receipt of Disability Living Allowance. The education domain included indicators of educational attainment at Key Stages 2, 3 and 4, secondary school absence rates, and destinations of children at age 16. The crime domain included rates of burglary, theft, criminal damage and violence. Both the housing and environment domains included two equally weighted sub-domains relating to access and quality. Access to housing was indicated by overcrowding, shared accommodation, and homelessness. Quality of housing was indicated by lack of central heating. The environmental access sub-domain included the proximity of sports and leisure facilities within walking distance, and distance to school. Environmental quality was indicated by air quality, the percentage of green space and woodland, the number of bird species, and road safety measured through road traffic accidents. Due to missing data on the numbers of children served by local authorities at small-area level, the children (at risk of being) in need domain was modelled using the material and education domains of the CWI and the income and employment domains of the IMD 2007 [16
The percentage of Lower Super Output Areas (LSOAs, average populations of 1,500) in each PCT that were in the fifth quintile (lowest well-being) of the 32,482 LSOAs in England was calculated for six of the seven domains of the CWI 2009 (material; education; crime; housing; environment; and children (at risk of being) in need). As the health domain includes an EAR of children aged 0-18 in each LSOA as an indicator there is an in-built association with the EAR for children aged 0-14. This domain and the overall CWI measure incorporating this domain have therefore been excluded from our reporting in order to avoid an obvious bias.
Each PCT's 'local hospital' was defined as the hospital to which the largest percentage of children resident in each PCT was admitted.
Data were analysed descriptively using SPSS Release 15. Associations were measured using Kendall's taub correlation due to expectedly skewed distributions. Calculation of associations using Spearman's Rho correlation confirmed the pattern of these results.
The study was assessed as not requiring ethics approval by a NHS Research Ethics Committee.