Selecting a comparison group

Rushcliffe had relatively low rates of hospital admission before the enhanced support was introduced. Across the entire population (not just care home residents), in 2013/14, there were 776 emergency admissions for every 10,000 individuals living in Rushcliffe, compared with 891 for the average local authority in England. Compared with other areas of England, Rushcliffe also had relatively low levels of socioeconomic deprivation and low population density. Therefore, the Improvement Analytics Unit selected comparison residents from areas that had similar demographic and socioeconomic characteristics and emergency admission rates to Rushcliffe: Harborough, Blaby, Test Valley, South Cambridgeshire, Chelmsford and Brentwood. To the best of our knowledge, none of these were offering area-wide interventions like Principia’s enhanced support during the period concerned. The technical appendix contains more information on how the areas compared with Rushcliffe.

We applied the same inclusion and exclusion criteria to care home residents in the six comparison areas as we had to Principia residents. This produced a total of 2,957 residents aged 65 years or over from 93 care homes. From that wider group of care homes and residents, a matched subset of care homes and residents was identified that was similar to the Principia group on the following characteristics.

  • Care home characteristics: The number of beds in the care home; whether the care home was registered with the CQC as a nursing or residential home; whether the care home was registered as caring for additional population groups in addition to older people; whether the care home was in a rural or urban setting; the socioeconomic deprivation level of the local area.
  • Resident characteristics: Age; gender; ethnicity (white or non-white); particular health conditions associated with frailty (such as cognitive impairment, falls or significant fractures); particular health conditions that have been shown to be predictive of emergency hospital readmissions (such as chronic pulmonary disease and congestive heart failure); an index based on conditions that predict subsequent mortality (the Charlson index); and the number of emergency admissions, potentially avoidable admissions, nights in hospital, A&E attendances, elective admissions and outpatient attendances prior to moving to the care home.

The matched comparison residents were selected using genetic matching, which is a computer-intensive search algorithm that often produces more closely balanced groups than other methods. The approach ensured that the Principia and matched comparison residents moved into care homes at similar points in time, without seasonal differences in those admission dates.

We selected one matched comparison resident for each Principia resident, giving us 588 residents in the comparison group from 64 care homes.


These figures have been standardised for age based on the indirect method. The technical appendix contains more data on Rushcliffe and the comparison areas. See www.health.org.uk/publication/impact-enhanced-support-rushcliffe

** The technical appendix contains more information regarding how these variables were defined. See www.health.org.uk/publication/impact-enhanced-support-rushcliffe

†† The matching was done with replacement, meaning that a single comparison resident might be matched to more than one Principia resident. The group of 588 matched comparison residents consisted of 422 unique people.

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