The role of matched controls in building an evidence base for hospital-avoidance schemes: a retrospective evaluation

To test whether two hospital-avoidance interventions altered rates of hospital use: "intermediate care" and "integrated care teams."

Linked administrative data for England covering the period 2004 to 2009.

This study was commissioned after the interventions had been in place for several years. We developed a method based on retrospective analysis of person-level data comparing health care use of participants with that of prognostically matched controls.

Individuals were linked to administrative datasets through a trusted intermediary and a unique patient identifier.

Participants who received the intermediate care intervention showed higher rates of unscheduled hospital admission than matched controls, whereas recipients of the integrated care team intervention showed no difference. Both intervention groups showed higher rates of mortality than did their matched controls.

These are potentially powerful techniques for assessing impacts on hospital activity. Neither intervention reduced admission rates. Although our analysis of hospital utilization controlled for a wide range of observable characteristics, the difference in mortality rates suggests that some residual confounding is likely. Evaluation is constrained when performed retrospectively, and careful interpretation is needed.