A population-based cohort of people with rheumatoid arthritis in British Columbia was selected in 2002. Administrative billing data collected by the Ministry of Health of British Columbia to facilitate reimbursement for physician visits was used to identify all existing cases of rheumatoid arthritis treated between January 1996 and December 2000. For each patient, data on the use of all provincially funded health care resources, including hospital care, physician visits and prescribed medications dispensed by pharmacists, were obtained. Details of this cohort are described elsewhere.10
From the cohort data, we determined that the prevalence of rheumatoid arthritis in the BC population was 0.76%, which is consistent with prevalence rates of 0.5% to 1.1% (mean 0.8%) reported in epidemiologic studies of the condition.11
BC PharmaCare is British Columbia's drug benefit plan that assists provincial residents in paying for eligible prescription drugs and designated medical supplies. The plan provides residents different levels of coverage. At the time of the study, BC PharmaCare required that people aged 65 years and older pay 100% of the dispensing fees, but not the ingredient costs, to an annual maximum of $200. Once this deductible was reached, the drug benefit plan covered all dispensing fees and ingredient costs of drugs on the provincial formulary for the remainder of the year. PharmaCare has a Maximum Days Supply Policy to prevent wastage and stock-piling. For short-term or first-time drug prescriptions of maintenance drugs, the coverage is limited to a maximum 30-day supply, whereas repeat prescriptions of maintenance drugs are covered for a maximum 100-day supply.
For this study we selected elderly patients from the population-based cohort described earlier who had existing rheumatoid arthritis (diagnosed in the previous year or earlier) and who had reached the annual maximum co-payment of $200 for any calendar year from 1997 to 2000. For each patient selected, we included in the analysis only data for health care services used during the year(s) in which the annual maximum co-payment had been reached. Since the sample was selected on the basis of annual drug prescription records and the year rheumatoid arthritis was first diagnosed, the number of patients being selected differed from year to year.
The outcomes assessed were whether patients were admitted to hospital, the number of hospital admissions, the number of physician visits and the total number of prescriptions filled. All of these outcomes were measured for all care received.
We assessed the following variables for rheumatoid arthritis care as covariates: whether patients had been prescribed disease-modifying antirheumatic drugs (DMARDs), an important part of the medical treatment of rheumatoid arthritis; how long patients had the condition; whether patients were prescribed oral corticosteroid therapy during the study period; whether and how often patients visited an orthopedic surgeon; whether they had undergone orthopedic surgery; and the number of orthopedic procedures performed for rheumatoid arthritis.
For statistical analysis, we defined the period during which the annual maximum co-payment had not been reached as the “cost-sharing period” and the one beyond which the annual maximum had been reached as the “free period.” For each of the calendar years from 1997 to 2000, we compared the patients' utilization of all health care services between the cost-sharing and free periods.
For our analysis of the use of hospital services, we used a 2-part model. First, we compared the probability of a patient being admitted to hospital during the cost-sharing period with that of admission during the free period. For this analysis we used an estimated logistic regression analysis folowing the generalized estimating equations (GEE) approach (with an unstructured correlation matrix).12
Second, we studied the number of hospital admissions in a given year among the patients who were admitted during the year. To adjust for the different lengths of the cost-sharing and free periods, we used monthly figures. A paired sample comparison was performed for each year to assess the difference in monthly utilization of hospital services. The 95% confidence interval for each of the mean differences was estimated through bootstrap sampling. We also fitted a mixed-effect model with a random patient effect and fixed effects of period and year and other explanatory variables (e.g., age, sex, DMARD use, corticosteroid use, visits with an orthopedic surgeon and performance of orthopedic surgery). The covariate values were evaluated based on data since the beginning of 1996 to the end of the year before which the outcomes were evaluated. Utilization in a particular year, the dependent variable, was modelled to be dependent on covariates from the previous years except for the dummy variable indicating the cost-sharing period and the free period; therefore, utilization was based on data from 1997 to 2000, but covariates were evaluated using data from 1996 to 2000. Explanatory variables were retained in the final model if p
values for the β coefficients were less than 0.05.
We performed similar analyses on all outcomes, including the number of physician visits per month, the number of prescriptions filled per month and the number of prescriptions filled per physician visit.