Impact measures

Once the Improvement Analytics Unit was content that the matched comparison group was similar to the Principia residents, the unit proceeded to compare how often residents used hospital care. The following seven impact measures were assessed.

  • Attendances at A&E departments (which might not result in a hospital admission).
  • Emergency admissions (occurring through A&E departments, or via direct and urgent referrals from GPs and other health care professionals).
  • The subset of ‘potentially avoidable’ emergency admissions, based on a list of conditions considered to be manageable in community settings or preventable through good quality care (see Box 2).
  • Elective admissions.
  • Outpatient attendances.
  • The number of nights spent as a hospital inpatient, following either an emergency or elective admission. We expressed this as a percentage of the total length of stay in the care home, and excluded admissions where the person was admitted and discharged on the same day.
  • The percentage of deaths that occurred outside of a hospital. We included this metric because the enhanced support included an element of end-of-life planning.

Hospital utilisation was measured for the period during which individuals were resident in care homes, counted from the month during which they moved into the care home to the month they departed. We tracked hospital utilisation until August 2016, so the analysis considered between 1 and 23 months of utilisation, depending on when the person joined (and left) the care home. On average, we followed Principia residents for 211 days (standard deviation 178 days), and matched comparison residents for 201 days (standard deviation 177 days).

Comparisons between the Principia residents and the matched comparison group were made using multivariable regression. The regression models were not strictly necessary, since the matched comparison and Principia residents already had similar baseline characteristics. However, some small differences remained even after matching, and the regression models adjusted for those. Matching and regression generally perform better in combination than separately. The regression models produced a ‘best estimate’ of the relative difference in hospital utilisation between the Principia residents and the matched comparison group, together with a 95% confidence interval.

The analysis was conducted in line with a statistical analysis plan, which was discussed with a Technical Advisory Group and finalised before the data analysis began.


‡‡ We included attendances at specialty A&E departments and minor injury units as well as major A&E departments. However, for this population, virtually all the A&E activity occurred in major departments.

§§ For the number of A&E attendances, emergency admissions, potentially avoidable emergency admissions, elective admissions and outpatient attendances, the models produced ‘rate ratios’. For the percentage of nights spent in hospital and the percentage of deaths that occurred outside hospital, the estimates refer to a slightly different quantity, namely odds ratios.

¶¶ There were some minor deviations from the statistical analysis plan, for example, in the covariance structure assumed in the regression modelling. These are unlikely to have had a qualitative impact on the findings. Full details are available on request.

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