The questionnaire administered to patients at both baseline and follow-up included 4 scales measuring features of the physician-patient relationship (quality of communication, interpersonal treatment, physician’s knowledge of the patient, and patient trust) and 4 scales measuring structural aspects of care (access to care, visit-based continuity, duration of primary care relationship, and integration of care). The 8 scales are part of the Primary Care Assessment Survey (PCAS), a validated questionnaire with measures corresponding to the defining features of primary care posited by the Institute of Medicine (IOM). All concepts are measured in the context of a specific physician-patient relationship and reference the entirety of that relationship (ie, they are not visit-specific). All PCAS scales are scored on a 0 to 100 scale, with higher scores indicating more of the referent attribute. Details of the development and psychometric performance of the PCAS scales are available elsewhere. The item content and reliability coefficient (Cronbach a)for each scale are summarized in the Appendix Table 2A. In addition to completing the PCAS items referencing their experiences with and assessments of their primary physicians, the respondents also provided their physicians’ names.
Using the physician-identifying information provided by the patients, we linked data from the Massachusetts Board of Registration in Medicine (BRM) to the study database. The BRM data provided the physician’s practice address and several characteristics of the physician’s training and practice. We linked with the BRM data by using a matching algorithm based on the spelling of the physician’s name as provided by the patient, the distance between the patient’s home ZIP code and the physician’s practice site (BRM database), and the physician’s medical specialty. At both baseline and follow-up, matches from the BRM data were identified for 94.0% of the patients who named a physician.
Identifying Voluntary Versus Involuntary Disenrollment
Patients were classified as having changed physicians during the study period if their follow-up questionnaire reported having been in their primary physician’s practice for less than 3 years and if the physician named at follow-up was different from the one named in 1996. Those who changed physicians were then classified as having switched either voluntarily or involuntarily. A switch was considered involuntary if: (1) the patient’s baseline physician was no longer listed as active in the Massachusetts BRM database (n=77), (2) the baseline physician had moved more than 10 miles (n=91), or (3) the patient had moved more than 15 miles from the baseline residence (n=62).
In addition we considered the possible involuntary nature of physician switches that occurred along with a change in health plan enrollment. Because the employer in our study did not force or even incentivize health plan changes during the study period (ie, there was a consistent offering of health plans and no notable changes in the employee contributions for coverage), respondents who were insured by the commonwealth throughout the study period did not incur any involuntary physician switching owing to employer-imposed health plan changes. Among respondents not insured by the commonwealth throughout the study (ie, respondents who left state employment [n=40] or deferred coverage [n=7]), there were 6 who changed physicians. Five of these did so while remaining in the same health plan and were thus coded as having voluntarily changed physicians. The remaining individual who both changed health plans and physicians was dropped from our analysis of voluntary disenrollment, since we were unable to ascertain whether the plan change forced a change in physician.
Statistical Analyses
We limited the analytic sample to patients who completed both the baseline and follow-up questionnaire, who identified a primary physician at baseline for whom a BRM database match was found, and who had either remained with their baseline physician throughout the study period or had voluntarily left the physician’s practice (n=3052). Patients who had involuntarily disenrolled from their baseline physician’s practice (n=230) were excluded. Their exclusion was necessary, since there was no way to determine whether those who involuntarily switched physicians would have otherwise voluntarily left their physician. The sociodemographic and health profile of the analytic sample (n=3052) did not differ from that of the complete 1999 sample (n=4108).
Multiple logistic regression methods were used to evaluate interpersonal and structural features of care, as measured by the baseline PCAS scales, as predictors of voluntary disenrollment from a physician’s practice. All scales were standardized ([X1-mean]/standard deviation) to permit direct comparison of results across scales. First, the 8 PCAS scales were tested individually as predictors of voluntary disenrollment. Testing scales independently in this way is useful in cases such as this where moderate to high correlations exist among some scales. Although the majority of PCAS scale correlations are small, higher correlations exist among some scales (r=0.40-0.86). We applied the Bonferroni correction for multiple comparisons to this set of analyses.