Using a geographical information system to map the distribution of dentists in Ohio
LOUIS SUSI, B.A. and
ANA KARINA MASCARENHAS, B.D.S., Dr.P.H.
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ABSTRACT
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Background. Studies have reported that dental care is the highest unmet health care need in the United States and have evaluated this in terms of individual determinants of access and utilization. None of these studies took into consideration the provider issues of availability and accessibility or of spatial relations. The aim of this study was to analyze issues of provider availability and accessibility in Ohio using a geographical information system, or GIS.
Methods. Three Ohio databases were geocoded using GIS software. The databases included all 6,132 dentists licensed to practice in Ohio, 1,898 dentists who had billed the state Medicaid program in 1998 and safety-net clinics that provided free or low-cost care. Each practitioner was mapped at the county and ZIP code levels.
Results. Results are reported using maps at the county and ZIP code levels. The maps showed that 69.4 percent of dentists practiced in 12 metropolitan counties, 14 percent in 17 suburban counties and 16.6 percent in 59 rural counties (rural non-Appalachian counties plus Appalachian counties). In Appalachia, the dentist-to-population ratio was about one-half that of the metropolitan counties.
Conclusion. Obvious disparities exist in the distribution of dentists in Ohio, particularly in rural and Appalachian counties. The need to increase the availability of dentists in these counties is evident.
Practice Implications. GIS is a useful tool for evaluating provider distribution and availability and planning programs to attract dentists to areas with small numbers of dentists.
Dental diseases, such as periodontal disease, have been linked to various systemic diseases, such as cardiovascular disease, and low-birthweight babies.1–3 Prevention of oral diseases and maintenance of good oral health is dependent in large part on a person being able to access dental care. Regular dental visits provide an opportunity for dental health care professionals to provide preventive services and early diagnosis and treatment of oral conditions. People who do not receive regular dental care may be at an increased risk of developing serious oral disease sequelae that may affect their general health directly or indirectly. Guidelines from organizations such as the U.S. Department of Health and Human Services4 and the American Cancer Society5 recommend an annual dental examination; the Healthy People 2010 objectives6 recommend increasing the proportion of children and adults using the dental care system during each year from 44 percent to 56 percent.
A geographical information system is a useful tool for evaluating provider distribution and availability.
The literature has demonstrated consistently that children living in poverty have more tooth caries than do their more affluent peers because of dietary, behavioral and environmental factors. The children with the greatest dental treatment needs, however, have the least access to dental care.7 This disparity between the presence of dental disease and access to care is increasing despite public health and dental care programs for poor children.
Few studies have reported on access to dental services in the United States for children and adults.7–11 The greatest barriers to health care—including dental care—are experienced by minorities, the poor, the uninsured and people who are in relatively poor health.7–10,12 In addition to the individual patient’s characteristics that determine or predict access to dental care, other factors such as provider factors have been evaluated more recently. For example, low-income people in particular have difficulty finding dentists who will treat them or their children and frequently have to travel significant distances to get the care they need.11
The results of several studies reporting unmet dental needs are an indicator of poor access to dental care.7–9,13 Results of the 1994 Robert Wood Johnson Foundation National Access to Care Survey showed that 16.1 percent of respondents reported unmet health needs, with unmet dental needs being the highest at 8.5 percent.9 This represents 21 million Americans who had unmet dental needs in 1994.
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Dental access in Ohio.
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Access to dental care in Ohio is not much different than that in the rest of the United States. Surveys conducted in Ohio have demonstrated that dental access is an issue. In 1998, the Ohio Department of Job and Family Services reported that less than one-third of Ohio dentists filed a Medicaid claim.14 This low rate was expected, as many dentists are unwilling to accept Medicaid patients. Preliminary analyses of the Ohio Family Health Survey have demonstrated that dental care access is a problem in Ohio, with unmet dental needs being the greatest of the reported unmet health care needs in adults and children.15 Preliminary findings from a recent study of the transition of poor children in Ohio from private to public health insurance highlighted the need for access to dental care in under-served areas (Gilbert Nestel, M.S., unpublished data, March 2000).
In a preliminary descriptive analysis of the Ohio Family Health Survey data, variability in dental care access and utilization were observed, which raises several questions about factors that influence dental care utilization, as well as equity of access to dental services for the people of Ohio.15 In the bivariate analyses, dental care utilization (defined as at least one dental visit in the past 12 months) was found to be substantially lower in the elderly, in those whose income was less than 300 percent of the federal poverty level, in those living in Appalachian counties and in those with no dental insurance during the past year. More adult and child respondents reported a greater need for dental care than for any other unmet service need (Table 1
).15
To date, knowledge in the field of dental care access, utilization and unmet needs has focused on the general population16,17 and on specific populations such as African-American and Hispanic subgroups,12,18 people who have human immunodeficiency virus19–22 and older adults.23–26 All of these studies evaluated individual determinants or predictors of access and use. None, however, took into consideration the issues of provider availability and accessibility, or spatial relations such as the distance needed to travel to acquire dental treatment or time spent to get to a dental office.
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Geographical information systems.
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Research in medical-social geography involving spatial research into the location, planning and utilization of heath care facilities, as well as the identification of the features of health care delivery systems that influence their efficiency and effectiveness, is not new. Because of technological advances, however, existing methodologies can be applied easily, leading to sharper diagnostic measures. Geographical information systems, or GIS, are one such technology. GIS is a computer-based system used to map, store, retrieve and manipulate spatially referenced data.27 GIS allows users to simultaneously display a variety of data on multiple maps to determine possible spatial relationships.28 This analytical technique has been used for a variety of medical purposes, such as determining appropriate air and ground zones that would minimize transport time for trauma patients,29 studying access to medical care, allocating medical offices30 and assigning patients to offices.31
A review of the current literature did not reveal a similar study that reported the use of GIS in dentistry. We conducted this study to develop an approach for analyzing the variability, availability and accessibility in the distribution of dentists throughout Ohio.
The first step was to map the location of Ohio dentists at both county and ZIP code levels. Then we evaluated the availability of dentists to the low-income population by mapping safety-net clinics and dentists who accepted Medicaid.
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METHODS
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After reviewing studies that used GIS in other fields, including medicine, and reviewing available dental resources, we identified three databases of Ohio dentists for this study. We determined that the most complete data source for all Ohio dentists was the database maintained by the Ohio State Dental Board that contained 1998 data. It included all 6,132 dentists who were licensed to practice in Ohio, including data on dentists’ practice locations, with ZIP code and county information. The second database was from the Ohio Medicaid program and included the 1,898 dentists who billed the Medicaid program in 1998. The third database was of safety-net clinics that provide free or low-cost dental care; it was maintained by the Ohio Department of Health. We used the Medicaid and safety-net clinic information to help analyze the availability issues of poorer patients who did not have private insurance or the financial resources to pay for dental care out of pocket.
The three databases were merged using GIS software (ArcView, Version 3.2, Environmental Systems Research Institute Inc., Redlands, Calif.). The software also was used for geocoding and mapping purposes. (Geocoding is the assignment of spatial coordinates based on a given street address, county or ZIP code so that the location can be referenced by GIS and simultaneously displayed on a map.) GIS allowed us to display simultaneously these three sets of data on a single state map after they had been geocoded. GIS also generated maps at both the county and ZIP code levels, graphically plotting the distribution of dentists, Medicaid providers and safety-net clinics in Ohio.
We also studied the regional inequalities in the distribution of dentists across Ohio such as differences between urban and rural areas, differences between metropolitan and nonmetropolitan areas, and discrepancies between Appalachian and non-Appalachian counties. We did this by adding attributes such as Appalachian, rural non-Appalachian, suburban and metropolitan to the ZIP code and county layers. Counties were classified based on the regional classifications used by the Ohio Family Health Survey: Appalachian, rural non-Appalachian, suburban and metropolitan.
The Ohio dentist-to-population ratio at the county and regional subgroup levels were calculated and mapped. Estimates of the U.S. population for the same time frame were obtained from the U.S. Census Bureau.32
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RESULTS
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We reported the results by primarily using maps at the county and ZIP code levels. Figure 1 is a map of Ohio depicting all 88 Ohio counties. The maps illustrate various regional distributions of dentists and show every licensed-to-practice dentist in Ohio. After geocoding the 6,132 dentists from the Ohio State Dental Board database, we had a 99.8 percent match rate, allowing us to map 6,120 dentists by county and 6,122 by ZIP code.
Figure 2 reports the distribution of dentists by county. When the Ohio counties were categorized as metropolitan, suburban or rural, the maps demonstrated that 69.4 percent of dentists practiced in 12 metropolitan counties, 14 percent in 17 suburban counties and 16.6 percent in 59 rural counties (rural non-Appalachian and Appalachian). Further, while there were no counties in Ohio without a practicing dentist, counties such as Monroe, Morgan, Noble and Vinton each had two or fewer dentists practicing in the county.
Figure 2
also shows the distribution of dentists in Appalachian and non-Appalachian regions. Although Appalachian areas compose 35 percent of the state’s total landmass and 13 percent of Ohio’s population lives in Appalachian counties, only 7.6 percent of Ohio’s dentists practice in Appalachian counties. The counties we previously mentioned as having two or fewer dentists all were Appalachian counties.
In Figure 3, all three databases—dentists who were licensed to practice in Ohio, dental providers who billed the Ohio Medicaid program and the safety-net clinics—were displayed simultaneously using GIS. The counties with the highest number of dentists—Cuyahoga, Franklin and Hamilton—also were the counties with the highest number of Medicaid providers and safety-net clinics. In some rural counties such as Monroe and Morrow, none of the dentists billed Medicaid, while in Jackson, Meigs, Noble and Vinton counties—all of which are Appalachian counties—100 percent of dentists billed Medicaid in 1998.
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Figure 3. Distribution of Ohio dentists, including Medicaid and safety-net providers, at the county level. One dot (•) = 2 Medicaid providers.
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The difference in the proportion of dentists billing Medicaid among the four county subtypes was noteworthy. The proportion of dentists billing the Ohio Medicaid program in Appalachian, rural non-Appalachian, suburban and metropolitan counties was 49 percent, 39 percent, 29 percent and 28 percent, respectively. On average, the proportion of Ohio dentists billing Medicaid was 31 percent in 1998.
Figure 4 presents the same data as Figure 3 for dentists and Medicaid providers but at the ZIP code level. Interestingly, there were many ZIP codes across Ohio that did not have any dentists including some within Cuyahoga, Franklin and Hamilton counties, which had the highest density of dentists.
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Figure 4. Distribution of Ohio dentists, including Medicaid providers, at the ZIP code level. One dot (•) = 2 Medicaid providers.
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When we compared the regional subgroups by dentist-to-population ratio, we found troubling results (Table 2, page 641). In Appalachia, the dentist-to-population ratio in 1998 was the highest at 1:3,146, which was about one-half that of Ohio’s metropolitan counties where the dentist-to-population ratio was 1:1,479. As we expected, the dentist-to-population ratio in rural non-Appalachian counties (1:2,839) and suburban counties (1:2,249) fell between the ratios for the Appalachian counties and the metropolitan counties. Overall, the average dentist-to-population ratio for Ohio was 1:1,836.
Figure 5 depicts the dentist-to-population ratio at the county level. It clearly demonstrates the discrepancy in the availability of dentists among counties. If we had mapped this at the ZIP code level, the disparities would have been more apparent.
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DISCUSSION
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Previous research in dentistry has shown that redistribution of resources to areas that need them probably will have a more immediate effect on dental health than will a policy of changing the public’s attitudes through dental health education.21 As the U.S. population is living longer and retaining its teeth longer, dental care access and use represent an important component of the health care process.
One important aspect of dental care access that has not been explored extensively is provider availability. In this study, we analyzed this feature of dental care accessibility and developed a plan to explore the distribution of dentists throughout Ohio. GIS is an analytical tool that has been used in a wide variety of health care fields and industries but only sparingly in dentistry. Using GIS, we were able to map and explore the inequalities of availability of dental care at both county and ZIP code levels, as well as for regional subgroups.
Our results show many facts about the spatial distribution of dentists in Ohio, as well as the regional inequalities in provider availability. One fact is that the dentist-to-population ratio in Appalachian counties was about one-half that found in metropolitan counties. In a national comparison of this statistic, Ohio fared poorly. The average dentist-to-population ratio in Ohio was 1:1,836 people in 1998, whereas nationally it was 1:1,700 people in 1999 as stated in the U.S. surgeon general’s report on oral health.33 In addition, though Appalachian and metropolitan counties both had similar proportions (11 percent) of Medicaid-eligible people, we found an obvious discrepancy between Appalachian counties, in which 49 percent of the dentists billed Medicaid, and metropolitan counties, in which 28 percent of the dentists billed Medicaid in 1998.
When the nine most-populated counties that had the largest number of dentists were compared with the remaining 79 counties, we found that the nine counties composed 52 percent of Ohio’s population and approximately 65 percent of its dentists, leaving 35 percent of dentists to care for 48 percent of the population throughout the rest of Ohio. Based on these findings, it may seem that dentists have chosen to locate their practices in the most densely populated areas rather than where dental care is needed most.
We also found that there were ZIP codes without a single dentist in them, even in metropolitan counties This shows that although the county-level map may display an adequate number of dentists, the ZIP code–level map shows disparities and access issues. These data alone show that there is a dilemma with regard to the availability of dentists, and possibly, accessibility to dental care.
The use of GIS in this project aided us in graphically presenting the distribution of dentists throughout Ohio. But more importantly, it laid the framework for future analysis of access to dental care and unmet dental need within Ohio.
According to the recent surgeon general’s report on oral health, a dilemma faced the U.S. population as it entered the 21st century.33 Beginning in 2000, the total number of practicing dentists began to decrease, as a greater number of dentists began retiring (estimated to be 2,500 to 4,300 or more per year between 1996 and 2021) than the number graduating from dental school (estimated at 4,000 per year). The number of students taking the dental admissions test, as well as that applying to dental school, has been declining since 1998.33 These data depict a grim view for the U.S. population in general and an even worse scenario for those living in regions that already have too few dentists.
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CONCLUSION
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From our results, we conclude that obvious disparities exist in the distribution of dentists in Ohio, particularly in the rural non-Appalachian and Appalachian counties. The need to increase the availability of dentists in such areas is evident and immediate.
Based on the results of this project, we recommend that Ohio set forth an incentive program to attract dentists to these areas. For example, tuition reimbursement programs could be instituted in exchange for service contracts to the regions deprived of dental care. Such a program would be beneficial to everyone involved.
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FOOTNOTES
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The authors thank Mark W. Horner, Department of Geography and the Center for Urban and Regional Analysis, The Ohio State University, Columbus, for his assistance with the geographical information system, as well as commentary on the manuscript.
An earlier version of this article was presented at the American Academy of Public Health Dentistry’s conference in Portland, Ore., in April 2001.
Mr. Susi is a third-year dental student, College of Dentistry, The Ohio State University, Columbus.
Dr. Mascarenhas is an associate professor and director, Division of Dental Public Health, Department of Health Policy and Health Services Research, 715 Albany St., B-306, Boston, Mass. 02118-2526, e-mail "karinam{at}bu.edu". Address reprint requests to Dr. Mascarenhas.
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ABSTRACT
Dental access in Ohio.
