Earlier studies have found that areas with higher primary-care physician-to-population ratio enjoy better health indicators than areas with lower primary-care physician-to-population ratio (Shi 1992
; Farmer, Stokes, and Fisher 1991
). Recent studies have also demonstrated that primary care was significantly associated with better health outcomes even after controlling for income inequality and other sociodemographic correlates of health (Shi et al. 1999
; Shi and Starfield 2000
). The current study affirmed previous research demonstrating a significant association of primary care supply and positive perceived health status (Starfield 1992
; Institute of Medicine 1994
; Shi 1992
; Politzer et al. 1991
; Bindman, Grumbach, and Osmond 1996
; Roos 1979
; Greenfield, Rogers, and Mangotich 1995
; Green 1996
; Grumbach 1996
; Donaldson and Vanselow 1996
). Moreover, rather than only using unidimensional proxies such as clinicians' primary-care specialties, the current study followed the IOM's definition and further operationalized primary care as multidimensional so that primary care can be captured more precisely.
The results of the study indicated a significant, deleterious association of income inequality with self-rated health and advanced earlier findings regarding the health benefits of primary care. Among individuals with a primary-care physician as their usual source of care, those experiencing better primary care, in particular enhanced accessibility and interpersonal relationship, reported better health both generally and mentally, than those experiencing worse primary care. Stratified analyses indicate that good primary-care experience (with primary-care experience score at mean or above versus below the mean) accounted for 5.29 percent reduction in individuals reporting bad health and 6.07 percent reduction in individuals reporting feeling depressed. The best primary-care experience (with primary-care experience score at top 25 percent versus bottom 25 percent) accounted for an 8.19 percent reduction in individuals reporting bad health and a 10.62 percent reduction in individuals reporting feeling depressed.
That socioeconomic status measures attenuate, although do not eliminate, the effect of both income inequality and primary care on self-rated health suggests that both income inequality and primary care are independently related to health. The finding that primary-care experience is significantly associated with self-rated health contributes to the mounting evidence that specific aspects of health services have an independent effect in improving population health (Starfield 1998
; Lantz et al. 1998
; Bunker, Frazier, and Mosteller 1994
), in particular, the beneficial effects of primary care.
Moreover, good primary-care experience was able to reduce the adverse impact of income inequality on health as disparities in self-rated health decreased between higher and lower income-inequality areas (e.g., the odds ratio in the most egalitarian areas relative to the least egalitarian areas dropped from 1.71 when only Gini was in the model to 1.59 when primary-care experience was added to the model). Those experiencing high quality primary care in higher income-inequality areas may be able to address many of the health concerns in a more timely and effective manner than those experiencing poor quality primary care. However, because they generally experience more health problems than individuals in more egalitarian areas, they remain less healthy than individuals experiencing good quality primary care in more egalitarian areas. Thus, good primary-care experience served as a buffer that moderates, although does not eliminate, the adverse impact of income inequality.
Although good primary care did not have a significant association with reducing differences in feeling depressed between high and low income-inequality areas, it had large and significant coefficients reflecting a strong and inverse independent association with feeling depressed. This could also be due to the strong adverse impact of income inequality on mental health. Kawachi and Kennedy (1999)
suggested that one pathway linking income inequality to health is via the psychosocial effects of frustrated social comparisons (p. 48). They cited studies that demonstrate the effects of relative deprivation on levels of frustration that have adverse health consequences. This study also indicates that the increased presence of primary-care physicians operates primarily through better primary-care services, because its effect is small when more proximate measures of primary care are included in the analysis.
In addition to primary-care experience and income inequality, socioeconomic characteristics remained critical in influencing individuals' health. In particular, both education and income had a gradient association with general health and feeling depressed. It is noteworthy that the straight progressive influence of income inequality is disrupted when these variables are added to the model. Thus, from a policy perspective, improvement in individuals' health is likely to require a multipronged approach that addresses individual socioeconomic determinants of health and social and economic policies that affect income distribution, as well as improves primary-care experience of health services to buffer the health effects of income inequality.
Caution needs to be exercised in interpreting the results of the study. The analyses presented reflect association rather than causality. Causal relationships between primary-care experience and self-rated health are difficult to identify with certainty due to the largely cross-sectional nature of the dataset. However, when primary care is assessed by these measures of primary care adequacy, they provide no basis for expecting that people's health should influence their choice of primary-care provider. Although there may be reverse effects regarding access to care (wherein sicker people might be likely to select more accessible providers), the findings indicate that the effect of primary care is consistent across the attributes that were assessed. Furthermore, the absence of effect of continuity (duration with the physician) suggests that prior health is not a major factor, as those with poorer health might be expected to stay a shorter time with a practitioner than others, because of their actual or perceived need for a more varied set of services.
In this study, we were unable to distinguish between physicians who were primary-care generalists from those who focused on a subspecialty. However, our findings indicate that it is not merely specialty that determines quality of primary-care practice but, rather, the particular primary care–oriented nature of practice that accounts for the results.
The inability of the research to assess quality of primary care using a suboptimal instrument may underestimate the magnitude of differences associated with high-quality primary care. The paucity and incompleteness of the primary-care measures in the dataset precluded us from considering all the major measures of primary-care domains, in particular, those reflecting comprehensiveness, coordination (Safran et al. 1998
; Flocke 1997
; Starfield et al. 1998
), or family and community focus (Institute of Medicine 1994
). The measures used by the Community Tracking Study cover only two of the attributes of primary care, and even these are only approximations of the complexity of primary-care attributes. The availability of a well-validated tool of measurement is critical in exploring the quality of primary care. Fortunately, such measures are now available for administration to community and enrolled populations (Safran et al. 1998
; Cassady et al. 2000
; Shi, Starfield and Xu 2000
). When such measures are used, better delineation of primary-care practice and exploration of differences is facilitated. For example, two previous studies using the Primary Care Assessment Tool (PCAT) instrument showed differences in achievement of many of the primary-care attributes in HMOs and fee-for-services facilities (Starfield et al. 1998
; Shi et al. 2000
Another limitation of the primary-care experience measures that were used in the dataset include their restriction to people's judgments about the primary-care attributes rather than their experiences with them. The response categories (except for the access items) required people to judge whether the attribute was poor to excellent (5 categories) or whether they were satisfied with them (5 categories). In contrast, primary-care instruments such as the PCAT elicit actual experiences rather than satisfaction with them. This may explain the lesser impact in this study (as compared with the others) of primary care and income inequality on depression, as people with depression may have different expectations of their experience than others and therefore report on them differently.
A further measurement-related limitation is the classification of usual source of care provider as primary-care doctors and specialists, which does not allow the identification and inclusion of certain specialists (such as obstetricians and gynecologists) who might provide some aspects of primary health care.
Further progress of research will be made by incorporating better measures of the primary-care domains and delineating the pathways through which good primary-care experience attenuates the adverse health effects of income inequality. Longitudinal data would be necessary to yield conclusive findings and determine the nature and direction of effects.