the extent that they are correlated with the observed ones. Five strata suffice to Ž
remove over 90 of the bias for each of the variables Rosenbaum and Rubin, .
1984 . Patients were, therefore, assigned to strata based on the quintiles of the propensity score. Univariate analyses of the covariates were performed to ensure
that within each stratum, there was no appreciable difference between the patient groups, by discharge strategy. Tests of significant differences for continuous data
were based on t-tests and analysis of variance. Fisher’s exact tests and chi-square tests were used for binary and nominal variables. Statistical analyses were
Ž performed on a Sun Sparc Server 1000 using SAS release 6.11 SAS Institute,
. Cary, NC .
The treatment cost and patient outcome due to each discharge strategy where calculated within each stratum. To estimate the treatment costs and outcomes for
the entire patient population, weighted sums of the stratum-specific results were Ž
. calculated, using standard methods for stratified sampling Jessen, 1978 . The
end-product of the propensity score analysis was an estimate, for each discharge strategy, of the average cost and the readmission rate had all patients in the
province received that treatment following discharge. Standard deviations of the estimates were also obtained, allowing the calculation of P-values in order to test
for significant differences between the discharge destinations. To adjust for multiple comparisons of discharge destinations, individual pairwise comparisons
Ž .
considered P-values - 0.0083 0.05r6 to be statistically significant. This adjustment yields an overall significance level of 0.05.
3. Results
Between FY91 and FY94, the number of JR hospitalizations in Ontario increased at an average annual rate of 5.5, which was less than half the annual
Ž growth rate of 11.5 recorded between FY81 and FY91 Cohen et al., 1994a,b;
. Coyte et al., 1996b; Naylor and De Boer, 1996 . Moreover, after adjusting for
population growth, the annual rate of growth in JR hospitalization rates was 3.8 Ž
. between FY91 and FY94 compared to 9.8 between FY81 and FY91 Fig. 1 .
3.1. Discharge strategies Study exclusion criteria resulted in a unique patient-level file comprised of
29,131 JR patients who were discharged to one of four destinations between FY91 and FY94: a rehabilitation hospital, and subsequently, to home without home care
Ž .
Ž .
RS ; a rehabilitation hospital, and subsequently, to home with home care RH ; Ž
. Ž
. home with home care HC ; and home with self-care or informal-care SC .
Despite deceleration in the growth of JR rates since FY91, there have been Ž
. notable modifications to JR discharge strategies Table 1 . The percentage of SC
Fig. 1. JR surgery rates in Ontario, FY1981–FY1994.
patients fell from 40.8 in FY91 to 28.8 in FY94, while the percentage of HC patients increased from 34.7 to 42.8. Since an additional 7.3 of all JR
patients received home care services following discharge from a rehabilitation hospital in FY94, more than half of all JR patients received home care services in
Ž . FY94 following their episode s of inpatient care.
While home care utilization by JR patients increased at an average annual rate of 10.8 and 12.5 between FY91 and FY94 for HC and RH patients, respec-
tively, there was also an increase in the utilization of rehabilitation hospitals. Specifically, the average annual rate of growth in the use of rehabilitation hospitals
Table 1 Number of JR patients by discharge destination, FY1991–FY1994
RSsRehabilitation and Self-Care; RH sRehabilitation and Home Care; SC sSelf-Care; HC s Home Care.
Fiscal year Discharge destination
RS RH
SC HC
All FY91
1337 405
2902 2473
7117 FY92
1429 551
2250 2799
7029 FY93
1501 503
2177 2955
7136 FY94
1646 576
2264 3363
7849 Ž
. Ž
. Ž
. Ž
. Ž
. FY91–FY94
5913 20.3 2035 7.0
9593 32.9 11,590 39.8
29,131 100.0
was 7.2 and 12.5 for RS and RH patients, respectively. Thus, the average annual rate of change in the use of home care services, rehabilitation hospitals, and
self-care since FY91 were 11.0, 8.5, and y7.9, respectively. These results demonstrate a shift towards greater reliance on home care services and inpatient
rehabilitation, and less reliance on self-care following an acute care JR hospitaliza- tion.
3.2. Characteristics of JR patients Table 2 reports JR patient characteristics by discharge destination. RH patients
Ž .
were significantly P - 0.0001 more likely to be female, older, exhibit a rela- tively high comorbidity index and be discharged from a non-teaching hospital than
other patients. These same characteristics distinguish patients discharged with Ž
. Ž
home care services HC and RH from those discharged without such services SC .
and RS . Moreover, SC patients form the antithesis to RH patients; they were Ž
. significantly P - 0.0001 more likely to be younger male patients, with relatively
few comorbid conditions, who were discharged from a teaching hospital. There Ž
. was a significant P - 0.0001 trend towards JR surgery on younger male patients,
with more comorbid conditions, who were discharged from non-teaching hospitals, with this trend common to all discharge destinations.
3.3. Index acute care hospitalizations Between FY91 and FY94, there was a dramatic decline in the duration of
Ž .
inpatient acute care for JR patients Table 3 . Specifically, the average length of stay fell by 21.0 from 12.4 days in FY91 to 9.8 days in FY94. This decrease,
which was similar for all discharge strategies, represents an average annual decrease in the duration of inpatient care of 7.5. Patients discharged to home
Ž .
Ž .
with home care HC experienced a significantly P - 0.0001 longer average
Table 2 Characteristics of JR patients by discharge destination, FY1991–FY1994
RSsRehabilitation and Self-Care; RH sRehabilitation and Home Care; SC sSelf-Care; HC s Home Care.
Patient characteristics Discharge destination
RS RH
SC HC
All Chi-square
P -0.0001 63.2
72.9 45.7
62.3 57.7
P -0.0001 Ž
. Age means
69.3 73.7
67.1 70.7
69.4 P -0.0001
Ž . Charlson 0
12.4 17.0
11.9 14.4
13.3 P -0.0001
Ž . Revision JR
2.3 3.0
2.2 2.2
2.3 P s 0.134
Ž . Teaching hospital
31.9 29.9
40.0 34.8
35.6 P -0.0001
Ž . Rural
7.0 12.4
14.0 15.6
13.1 P -0.0001
Table 3 Acute care length of stay for JR patients by discharge destination, FY1991–FY1994
RSsRehabilitation and Self-Care; RH sRehabilitation and Home Care; SC sSelf-Care; HC s Home Care.
Fiscal year Discharge destination
RS RH
SC HC
All FY91
12.2 10.3
12.2 12.9
12.4 FY92
10.9 11.4
11.3 12.2
11.6 FY93
10.3 10.9
10.2 11.3
10.7 FY94
9.7 9.5
9.3 10.3
9.8
length of stay than other JR patients even after controlling for potentially confounding variables, comprising patient age, gender, urbanrrural residence,
comorbidity, case mix group, type of procedure performed and hospital teaching status. After controlling for potential confounders, RH patients experienced a
Ž .
significantly P - 0.0001 shorter average length of stay than other JR patients. 3.4. Costs and outcomes after adjusting for assignment bias
Ž .
Fig. 2 reports the total cost in FY94 Canadian dollars of a continuum of JR care and acute care readmission rates by discharge destination over the study
period after controlling for various confounding variables. Standardized total costs, Ž
comprising the cost of acute care hospitalizations both index and subsequent
Fig. 2. Costs and outcomes of alternative discharge strategies for JR patients, FY1991–FY1994.
. readmissions , the cost of rehabilitation hospitalizations and the cost of home care
services, varied from a low of 8166 for SC patients to a high of 13,569 for RH patients.
Ž .
Patients discharged to rehabilitation hospitals RH and RS patients incurred Ž
. health system costs that were almost 5000 or between 50 and 60 greater
than either HC or SC patients. However, acute care readmission rates were 20.0 lower for RH patients than for HC patients, 266.5 per 10,000 JRs vs. 333.3, and
25.5 lower for RS patients than for SC patients, 201.9 per 10,000 JRs vs. 271.1. Thus, increased continuum of care costs associated with the use of rehabilitation
hospitals were associated with better health outcomes as measured through lower acute care readmission rates.
Patients discharged to home with home care either directly from an acute care Ž
. Ž
. hospital HC or after a rehabilitation hospitalization RH reported health system
Ž .
costs that were between 1000 and 400 or between 12.1 and 3.4 greater than either SC or RS patients. Acute care readmission rates were, 18.7 lower for
SC patients than for HC patients, 271.1 per 10,000 JRs vs. 333.3, and were 24.2 lower for RS patients than for RH patients, 201.9 per 10,000 JRs vs. 266.5. Thus,
Ž despite increased expenditures, adverse health outcomes measured by acute care
. readmission rates were greater for patients discharged with home care than for
patients without home care. While readmission rates were higher for some patients, the distribution of the reasons for readmission were similar for all JR
patients irrespective of their discharge destination.
Average health system costs fell at an average annual rate of 2.7 over the Ž
. study period. This annual reduction in costs was greatest for RS patients 4.2
Ž .
Ž .
followed by SC patients 3.7 , HC patients 3.5 , and finally, RH patients Ž
. 1.9 . The main reason for these reductions stem from the shorter duration of the
index acute and rehabilitation hospitalizations. Fig. 3 depicts the distribution of costs for JR patients by discharge strategy. The
share of index acute care costs ranged from a low of 56.1 for RH patients to a high of 97.9 for SC patients. However, there was very little variation in the
average cost of the index acute care hospitalization, which ranged from a low of 7616 for RH patients to a high of 8062 for RS patients. This lack of variation in
the cost of the index acute care hospitalization was also reported for rehabilitation hospital costs and home care costs. Rehabilitation costs were 4756 for RH
patients and 4881 for RS patients, while the cost of home care services were 908 for RH patients and 896 for HC patients. While acute care readmission
costs for all discharge strategies represented approximately 2.0 of total costs, these costs represented a larger share of such costs for JR patients discharged with
Ž .
Ž home care services HC and RH patients than patients without such services SC
. and RS patients . Our results suggest that variations in costs were primarily
attributable to variations in the propensity to utilize different packages of rehabili- tation care, rather than in variations in the cost of the services provided by these
rehabilitation programs.
Fig. 3. Components of costs for JR patients by discharge strategy, FY1991–FY1994.
3.5. Costs and outcomes Propensity scores were used to control for potential bias in the assignment of
discharge destinations. Although patients who were assigned to different discharge destinations had quite different characteristics, there were no appreciable differ-
ences within each stratum. Fig. 4 reports the total cost of a continuum of care and Ž
. acute care readmission rates. There were significant P - 0.0001 differences in
costs among the four discharge destinations. Costs ranged from 14,081 for RH patients to 8220 for SC patients. The acute care readmission rate per 10,000 JRs
for the relatively small number of RH patients was 373.6 and was not significantly different than those for other discharge strategies. Significant differences in acute
care readmission rates were recorded for comparisons between RS and HC
Ž .
Ž .
patients P s 0.002 , and RS and SC patients P - 0.0001 . In ascending order, these readmission rates per 10,000 JRs were 203.6 for RS patients, 284.4 for SC
patients, 344.4 for HC patients. Incremental cost–outcome analysis was performed to measure the potential
increase in continuum of care costs in order to lower acute care readmissions. Since RS patients recorded the lowest stratum-adjusted acute care readmission
rates, all comparisons included the RS discharge strategy. Moreover, as RH Ž
. patients were associated with significantly P - 0.0001 higher costs and greater
Ž .
readmission rates than RS patients P s 0.034 , the RH discharge strategy was not
Fig. 4. Costs and outcomes of alternative discharge strategies for JR patients, FY1991–FY1994.
assessed. Switching JR patients from a HC discharge strategy to a RS strategy results in increased continuum of care costs of 4058 per patient, a reduction in
readmissions of 140.8 per 10,000 JRs, and therefore, yields an incremental cost of each saved readmission of 288,210. Furthermore, switching from a SC discharge
strategy to a RS strategy results in increased continuum of care costs of 4942 per patient and a reduction in readmissions of 80.8 per 10,000 JRs. The incremental
cost of each saved readmission associated with this switch in practice was 611,634.
4. Discussion
