Estimation of excess risk of readmission to hospital after an index inpatient separation.
OBJECTIVE
To develop methods to measure excess risk of readmission following an index admission using linked administrative health data.


METHODS
The cumulative risk of readmission following an index admission was calculated for index and reference subjects using linked hospital morbidity, death, and electoral roll data in cohort, cohort-crossover, and cohort-comparison-crossover designs.


METHODS
Index subjects were defined as any man age 20 years or older who separated from an acute hospital in Western Australia in 1990 to 1995 following any form of prostatectomy for a principal diagnosis of benign prostatic hypertrophy. Reference subjects were selected from the general population and the electoral roll (cohort designs). Cases were also used as their own historical controls (cohort-crossover) with and without adjustment for background time difference (cohort-comparison-crossover).


METHODS
The excess risk of readmission following an index admission was estimated by calculating the cumulative risk of readmission in index subjects and subtracting the background risk of admission. The background risk calculation varied according to the study design.


RESULTS
The risk of readmission at 30 days increased by 241 to 328% following the procedure. After 1 year of follow-up, the risk of readmission was still increased by 58 to 108%. In general, the absolute differences between index and reference subjects decrease or remain the same with increasing rigor of the methods.


CONCLUSIONS
In this example, there was little difference between the cohort-crossover and the cohort-comparison-crossover designs, suggesting that the cohort-crossover method is a justifiable method in the absence of electoral roll controls.
Centre for Health Services Research, School of Population Health, University of Western Australia, Crawley, Australia. kate@dph.uwa.edu.au
Kate J
KJ
Brameld
C D'Arcy J
CD
Holman
D000328:Adult; D015331:Cohort Studies; D018592:Cross-Over Studies; D006302:Health Services Research; D006801:Humans; D008297:Male; D008498:Medical Record Linkage; D008875:Middle Aged; D010359:Patient Readmission / Q000706:statistics & numerical data*; D011468:Prostatectomy; D011470:Prostatic Hyperplasia / Q000175:diagnosis / Q000601:surgery*; D018570:Risk Assessment / Q000706:statistics & numerical data*; D014600:Utilization Review / Q000379:methods*; D014904:Western Australia / Q000453:epidemiology