PUBLIC HEALTH BRIEFS
Measuring the Supply and Demand For Dentists in a Population WILLIAM G. HENDERSON, MPH, PHD
Introduction A more precise methodology for measuring the supply and demand for dental services in the population is needed. The traditional approach for evaluating dental manpower needs in a given geographic area has been to compute a population-per-dentist ratio and then to compare the computed ratio with some norm, such as the same ratio for the state or nation. Use of the population-per-dentist ratio to detect surplus and shortage areas has several deficiencies: 1. The "ideal" population-per-dentist ratio is unknown, even on an average basis over a large population served by many dentists. Thus, the use of a normative value for population-per-dentist ratio is questionable; 2. Comparison of population-per-dentist ratios between populations makes the assumption that all dental practitioners are equally productive; 3. Comparison of the ratios aiso assumes that the dental demands of the populations are equal. A more refined approach to the detection of dental surplus and shortage areas has recently been suggested by Mumma.1 The purpose of this paper is to apply a modification of the Mumma approach to an existing population, the State of Iowa, and to correlate the results with those obtained from the population-per-dentist ratio and a dental busyness index.
Methods The three methods for estimating dental manpower requirements on an area basis are outlined in Table 1. The population-per-dentist ratio has already been discussed. The method suggested by Mumma has as the basic unit of measurement the number of patient visits per year. Independent estimates are made of the number of patient visits per year supplied by dentists and utilized by residents of a given area. The difference between these two estimates represents the number of dental visits utilized by the area population but not supplied by the area dentists (-) or vice versa (+). When the number of visits supplied differs from the number utilized, it is due to consumers crossing area boundaries to seek dental care. If the difference in number of visits is An earlier version of this paper was presented at the 102nd Annual Meeting of the American Public Health Association in New Orleans, LA, October 20-24, 1974, and was revised July, 1975 for publication in the Journal. Address reprint requests to Dr. Henderson, Associate Professor of Biostatistics, Division of Preventive and Community Dentistry, College of Dentistry, University of Iowa, Iowa City, IA 52242.
70
divided by the number of patient visits supplied per year by the average dentist, it can be converted into numbers of dentists. Concern might arise about the use of patient visits as a basic unit of measurement since individual patient sittings are quite variable in length and productivity. However, these variable factors should tend to balance out in the analysis, since large populations of patients and dentists are usually compared. A survey conducted by the National Center for Health Statistics2 found that the average resident of the North Central region of the United States utilizes 1.4 dental visits annually. Although utilization rates differ by age, education, etc., in the interest of simplification the regional figure was multiplied by the 1970 population of each county and region in Iowa to obtain estimates of the number of dental visits utilized. Estimates of the number of dental visits supplied were obtained from a 1973 Survey of Iowa Dentists conducted by TABLE 1-Three Measures of Dental Surplus/Shortage Areas 1. Population-per-dentist ratio for an area = Np ND Where NP = total population in the area ND = total number of dentists in the area
2. Number of dentists presumed needed to serve area (-) or presumed to be serving other areas (+) = PVPYsupplied by dentists - PVPYutilized by population PVPYsupplied by average dentist Where PVPY = patient visits per year PVPYutilized by population = 1 .4 x Np PVPYsupplied by dentists = (number of pMD (weeks in of, fice per yr.)i x patient visits supplied 1 per week)i
PVPYsupplied by average dentist = PVPY supplied by dentists ND
ND
3. Busyness index for an area = ~ (BI) i=1
ND where (BI)i = busyness index for the ith dentist 1, if the dentist was not busy enough and wanted more patients 2, if the dentist provided care for all who requested it, had enough patients and did not feel overworked 3, if the dentist provided care for all who requested it but felt overworked 4, if the dentist was too busy to treat all requests
AJPH January, 1976, Vol. 66, No. 1
PUBLIC HEALTH BRIEFS TABLE 2-Number of Dentists "Needed" (-) or in "Excess" (+) by Degree of Urbanization of County
Type of County
Number of Counties
Total Number of Dentists "Needed" (-) or in "Excess" (+)
Average Number of Dentists per County "Needed" (-) or in "Excess" (+)
7
+74.8
+10.7
14
+ 7.5
+ 0.5
78 99
-125.7 -43.4
-1.6
Containing SMSA Containing at least one community of 10,000 or more but no SMSA Containing no communities as large as 10,000 Total
the Iowa State Department of Health.3 Data were sought from all practicing Iowa dentists on number of weeks spent in the dental office and the average number of patient visits provided per week. An estimate of the number of patient visits provided per year was obtained from the product of these two numbers. Differences between estimated number of patient visits per year utilized and supplied were calculated. These differences were then divided by 3,355 (the number of patient visits supplied by the average Iowa dentist in 1973) to convert into number of dentists. The busyness index for an area was calculated by averaging the busyness indices for all dentists in the area obtained from the 1973 survey. The index for the individual dentist was self-reported on a scale from one to four, where the number "one" indicated that the dentist wished he had more patients and the number "four" indicated that the dentist was too busy to treat all patients requesting care. The data from the survey were relatively complete.3 The response rate was 1,300 respondents out of 1,441 questionnaires sent out, or 90.2%. One important factor affecting the large response rate was that the questionnaires were attached to license renewals. Nonrespondents to the questionnaire were followed up with telephone calls to obtain the required information.
Results The results of the analysis based upon patient visits showed a statewide "deficit of (-) 43 dentists," i.e. 43 out-ofstate dentists were helping to meet the dental needs of the state population. This represents a "deficit" of only 3.7%
when compared to the total number of practicing dentists in Iowa (1,147). The maldistribution of dentists appeared to be a more critical problem. The estimated number of dentists presumed needed or presumed serving other area needs ranged from (+)31 in one county to (-)6 in another county. Table 2 presents the number of dentists presumed "needed" (-) or in "excess" (+) according to the degree of urbanization of the county. Those counties containing a Standard Metropolitan Statistical Area (SMSA) had on the average 10.7 dentists "in excess" and presumably serving residents of other areas. The rural counties of Iowa containing no communities of 10,000 or more needed on the average 1.6 additional dentists to serve the county population, given current utilization rates.
This same analysis for the 16 planning regions in Iowa is presented in Table 3. The range was from 10 dentists in "excess" in one region to 23 dentists "needed" in another region. Regions containing a SMSA had an average "excess" of 1.6 dentists, and regions containing no communities of 10,000 or more had an average presumed "need" for 8.2 dentists. The three measures of dental manpower "needs" (population-per-dentist ratio, number of dentists "needed" or in "excess", and busyness index) were calculated for each county and region in Iowa. Tables 4 and 5 present the intercorrelations of these measures. The correlations were higher for the data by regions than for the data by counties, probably due to the reduction in extreme fluctuations on a regional basis as opposed to a county basis. The most important finding from this correlation analysis is that the measure of presumed surplus and shortage based upon patient visits was
TABLE 3-Number of Dentists "Needed" (-) or in "Excess" (+) by Degree of Urbanization of Region Average Number of Dentists Number of Regions
Total Number of Dentists "Needed" (-) or in "Excess" (+)
per Region "Needed" (-) or in "Excess" (+)
Containing SMSA Containing at least
7
+11.5
+1.6
one community of 10,000 or more but no SMSA Containing no communities as large as 10,000
6
-30.2
-5.0
3 16
-24.7 -43.4
-8.2
Type of Region
Total AJPH January, 1976, Vol. 66, No. 1
71
PUBLIC HEALTH BRIEFS TABLE 4-Intercorrelations Between the Three Measures of "Surplus/Shortage" Areas Based Upon the Data by Counties in Iowa (n = 99)
Busyness Index Population/Dentist Ratio Number of Dentists Needed
Number of Dentists Needed
Busyness Index
Population/ Dentist Ratio
1.00
0.01
0.16
1.00
0.38*** 1.00
The correlation is significantly different from zero at the level: *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001
TABLE 5-Intercorrelations Between the Three Measures of "Surplus/Shortage" Areas Based Upon the Data by Regions in Iowa (n = 16) Number of
Busyness Population/ Index Dentist Ratio
Busyness Index Population/Dentist Ratio Number of Dentists Needed
1.00
0.43 1.00
Dentists Needed
0.81*** 0.68** 1.00
not reflect the situation in the State of Iowa as in each of its counties. Furthermore, it is well known that dental need is considerably greater than dental demand, and service utilization. The methodology does have some advantages, however. It avoids the often stated concern of organized dentistry that planners base their estimates on the oral needs of people instead of on the services they will utilize. It also provides some assurance to dentists moving into the defined "shortage" areas that their services will be utilized. The results in this study pertain only to the current status of the supply and distribution of dentists in Iowa. The University of Iowa College of Dentistry has recently considerably increased its class enrollments which should help to alleviate the current dental manpower shortage. Furthermore, the more recent graduates tend to utilize auxiliaries more and thus should tend to be more productive in the long run. On the other hand, a significant number of Iowa dentists are approaching retirement age which will aggravate the problem. Furthermore, the steadily increasing proportion of the population covered under dental prepayment programs may increase the effective demand for dental services in the future. A longitudinal analysis of the supply and demand for dental services incorporating some of these factors is needed.
The correlation is significantly different from zero at the level: *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001
significantly more highly correlated with the dentists' own estimation of their busyness than was the population-per-dentist ratio (0.81 vs. 0.43 in the data by regions). This could be an indication that the measure based upon patient visits is a more valid measure of dental surplus and shortage areas than is the traditional population-per-dentist ratio.
REFERENCES
Discussion
1. Mumma, Richard D. Jr., "Report of the Manpower and Education Committee," Journal of Public Health Dentistry, 34:1:5255, Winter 1974. 2. U. S. Department of Health, Education and Welfare, Public Health Service, National Center for Health Statistics, Dental Visits: Volume and Interval Since Last Visit, United States-1969. Vital and Health Statistics, Series 10, Number 76, Washington, D. C.: Government Printing Office, July 1972. 3. Survey of Dentists, Iowa-1973. Iowa State Department of Health, Records and Statistics Division, Des Moines, Iowa, March 1974.
Although the methodology reported in this paper is probably an improvement over the traditional population-perdentist ratio, it has some limitations which should be mentioned. Demand was based upon a statistic reported for the North Central Region of the United States. This figure may
The author would like to thank Dr. John Goodrich of the Iowa State Department of Health for furnishing the data used to accomplish this study.
ACKNOWLEDGMENTS
(Briefs continued next page)
The attending women, possessed of the qualities described, shall instruct her as follows:-"Don't strain when there is no labor pain. For as regards a woman who strains in the absence of labor pains, her efforts are useless, her offspring becomes deformed or diseased or suffers from dyspnea, cough, dehydration and splenic disorders. from: The Caraka Samhita (Ayurvedic medicine) Shree Gulabkunverba Ayurvedil Society Jamnagar, India, 1949
72
AJPH January, 1976, Vol. 66, No. 1
Measuring the Supply and Demand For Dentists in a Population WILLIAM G. HENDERSON, MPH, PHD
Introduction A more precise methodology for measuring the supply and demand for dental services in the population is needed. The traditional approach for evaluating dental manpower needs in a given geographic area has been to compute a population-per-dentist ratio and then to compare the computed ratio with some norm, such as the same ratio for the state or nation. Use of the population-per-dentist ratio to detect surplus and shortage areas has several deficiencies: 1. The "ideal" population-per-dentist ratio is unknown, even on an average basis over a large population served by many dentists. Thus, the use of a normative value for population-per-dentist ratio is questionable; 2. Comparison of population-per-dentist ratios between populations makes the assumption that all dental practitioners are equally productive; 3. Comparison of the ratios aiso assumes that the dental demands of the populations are equal. A more refined approach to the detection of dental surplus and shortage areas has recently been suggested by Mumma.1 The purpose of this paper is to apply a modification of the Mumma approach to an existing population, the State of Iowa, and to correlate the results with those obtained from the population-per-dentist ratio and a dental busyness index.
Methods The three methods for estimating dental manpower requirements on an area basis are outlined in Table 1. The population-per-dentist ratio has already been discussed. The method suggested by Mumma has as the basic unit of measurement the number of patient visits per year. Independent estimates are made of the number of patient visits per year supplied by dentists and utilized by residents of a given area. The difference between these two estimates represents the number of dental visits utilized by the area population but not supplied by the area dentists (-) or vice versa (+). When the number of visits supplied differs from the number utilized, it is due to consumers crossing area boundaries to seek dental care. If the difference in number of visits is An earlier version of this paper was presented at the 102nd Annual Meeting of the American Public Health Association in New Orleans, LA, October 20-24, 1974, and was revised July, 1975 for publication in the Journal. Address reprint requests to Dr. Henderson, Associate Professor of Biostatistics, Division of Preventive and Community Dentistry, College of Dentistry, University of Iowa, Iowa City, IA 52242.
70
divided by the number of patient visits supplied per year by the average dentist, it can be converted into numbers of dentists. Concern might arise about the use of patient visits as a basic unit of measurement since individual patient sittings are quite variable in length and productivity. However, these variable factors should tend to balance out in the analysis, since large populations of patients and dentists are usually compared. A survey conducted by the National Center for Health Statistics2 found that the average resident of the North Central region of the United States utilizes 1.4 dental visits annually. Although utilization rates differ by age, education, etc., in the interest of simplification the regional figure was multiplied by the 1970 population of each county and region in Iowa to obtain estimates of the number of dental visits utilized. Estimates of the number of dental visits supplied were obtained from a 1973 Survey of Iowa Dentists conducted by TABLE 1-Three Measures of Dental Surplus/Shortage Areas 1. Population-per-dentist ratio for an area = Np ND Where NP = total population in the area ND = total number of dentists in the area
2. Number of dentists presumed needed to serve area (-) or presumed to be serving other areas (+) = PVPYsupplied by dentists - PVPYutilized by population PVPYsupplied by average dentist Where PVPY = patient visits per year PVPYutilized by population = 1 .4 x Np PVPYsupplied by dentists = (number of pMD (weeks in of, fice per yr.)i x patient visits supplied 1 per week)i
PVPYsupplied by average dentist = PVPY supplied by dentists ND
ND
3. Busyness index for an area = ~ (BI) i=1
ND where (BI)i = busyness index for the ith dentist 1, if the dentist was not busy enough and wanted more patients 2, if the dentist provided care for all who requested it, had enough patients and did not feel overworked 3, if the dentist provided care for all who requested it but felt overworked 4, if the dentist was too busy to treat all requests
AJPH January, 1976, Vol. 66, No. 1
PUBLIC HEALTH BRIEFS TABLE 2-Number of Dentists "Needed" (-) or in "Excess" (+) by Degree of Urbanization of County
Type of County
Number of Counties
Total Number of Dentists "Needed" (-) or in "Excess" (+)
Average Number of Dentists per County "Needed" (-) or in "Excess" (+)
7
+74.8
+10.7
14
+ 7.5
+ 0.5
78 99
-125.7 -43.4
-1.6
Containing SMSA Containing at least one community of 10,000 or more but no SMSA Containing no communities as large as 10,000 Total
the Iowa State Department of Health.3 Data were sought from all practicing Iowa dentists on number of weeks spent in the dental office and the average number of patient visits provided per week. An estimate of the number of patient visits provided per year was obtained from the product of these two numbers. Differences between estimated number of patient visits per year utilized and supplied were calculated. These differences were then divided by 3,355 (the number of patient visits supplied by the average Iowa dentist in 1973) to convert into number of dentists. The busyness index for an area was calculated by averaging the busyness indices for all dentists in the area obtained from the 1973 survey. The index for the individual dentist was self-reported on a scale from one to four, where the number "one" indicated that the dentist wished he had more patients and the number "four" indicated that the dentist was too busy to treat all patients requesting care. The data from the survey were relatively complete.3 The response rate was 1,300 respondents out of 1,441 questionnaires sent out, or 90.2%. One important factor affecting the large response rate was that the questionnaires were attached to license renewals. Nonrespondents to the questionnaire were followed up with telephone calls to obtain the required information.
Results The results of the analysis based upon patient visits showed a statewide "deficit of (-) 43 dentists," i.e. 43 out-ofstate dentists were helping to meet the dental needs of the state population. This represents a "deficit" of only 3.7%
when compared to the total number of practicing dentists in Iowa (1,147). The maldistribution of dentists appeared to be a more critical problem. The estimated number of dentists presumed needed or presumed serving other area needs ranged from (+)31 in one county to (-)6 in another county. Table 2 presents the number of dentists presumed "needed" (-) or in "excess" (+) according to the degree of urbanization of the county. Those counties containing a Standard Metropolitan Statistical Area (SMSA) had on the average 10.7 dentists "in excess" and presumably serving residents of other areas. The rural counties of Iowa containing no communities of 10,000 or more needed on the average 1.6 additional dentists to serve the county population, given current utilization rates.
This same analysis for the 16 planning regions in Iowa is presented in Table 3. The range was from 10 dentists in "excess" in one region to 23 dentists "needed" in another region. Regions containing a SMSA had an average "excess" of 1.6 dentists, and regions containing no communities of 10,000 or more had an average presumed "need" for 8.2 dentists. The three measures of dental manpower "needs" (population-per-dentist ratio, number of dentists "needed" or in "excess", and busyness index) were calculated for each county and region in Iowa. Tables 4 and 5 present the intercorrelations of these measures. The correlations were higher for the data by regions than for the data by counties, probably due to the reduction in extreme fluctuations on a regional basis as opposed to a county basis. The most important finding from this correlation analysis is that the measure of presumed surplus and shortage based upon patient visits was
TABLE 3-Number of Dentists "Needed" (-) or in "Excess" (+) by Degree of Urbanization of Region Average Number of Dentists Number of Regions
Total Number of Dentists "Needed" (-) or in "Excess" (+)
per Region "Needed" (-) or in "Excess" (+)
Containing SMSA Containing at least
7
+11.5
+1.6
one community of 10,000 or more but no SMSA Containing no communities as large as 10,000
6
-30.2
-5.0
3 16
-24.7 -43.4
-8.2
Type of Region
Total AJPH January, 1976, Vol. 66, No. 1
71
PUBLIC HEALTH BRIEFS TABLE 4-Intercorrelations Between the Three Measures of "Surplus/Shortage" Areas Based Upon the Data by Counties in Iowa (n = 99)
Busyness Index Population/Dentist Ratio Number of Dentists Needed
Number of Dentists Needed
Busyness Index
Population/ Dentist Ratio
1.00
0.01
0.16
1.00
0.38*** 1.00
The correlation is significantly different from zero at the level: *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001
TABLE 5-Intercorrelations Between the Three Measures of "Surplus/Shortage" Areas Based Upon the Data by Regions in Iowa (n = 16) Number of
Busyness Population/ Index Dentist Ratio
Busyness Index Population/Dentist Ratio Number of Dentists Needed
1.00
0.43 1.00
Dentists Needed
0.81*** 0.68** 1.00
not reflect the situation in the State of Iowa as in each of its counties. Furthermore, it is well known that dental need is considerably greater than dental demand, and service utilization. The methodology does have some advantages, however. It avoids the often stated concern of organized dentistry that planners base their estimates on the oral needs of people instead of on the services they will utilize. It also provides some assurance to dentists moving into the defined "shortage" areas that their services will be utilized. The results in this study pertain only to the current status of the supply and distribution of dentists in Iowa. The University of Iowa College of Dentistry has recently considerably increased its class enrollments which should help to alleviate the current dental manpower shortage. Furthermore, the more recent graduates tend to utilize auxiliaries more and thus should tend to be more productive in the long run. On the other hand, a significant number of Iowa dentists are approaching retirement age which will aggravate the problem. Furthermore, the steadily increasing proportion of the population covered under dental prepayment programs may increase the effective demand for dental services in the future. A longitudinal analysis of the supply and demand for dental services incorporating some of these factors is needed.
The correlation is significantly different from zero at the level: *0.01 < p < 0.05, **0.001 < p < 0.01, ***p < 0.001
significantly more highly correlated with the dentists' own estimation of their busyness than was the population-per-dentist ratio (0.81 vs. 0.43 in the data by regions). This could be an indication that the measure based upon patient visits is a more valid measure of dental surplus and shortage areas than is the traditional population-per-dentist ratio.
REFERENCES
Discussion
1. Mumma, Richard D. Jr., "Report of the Manpower and Education Committee," Journal of Public Health Dentistry, 34:1:5255, Winter 1974. 2. U. S. Department of Health, Education and Welfare, Public Health Service, National Center for Health Statistics, Dental Visits: Volume and Interval Since Last Visit, United States-1969. Vital and Health Statistics, Series 10, Number 76, Washington, D. C.: Government Printing Office, July 1972. 3. Survey of Dentists, Iowa-1973. Iowa State Department of Health, Records and Statistics Division, Des Moines, Iowa, March 1974.
Although the methodology reported in this paper is probably an improvement over the traditional population-perdentist ratio, it has some limitations which should be mentioned. Demand was based upon a statistic reported for the North Central Region of the United States. This figure may
The author would like to thank Dr. John Goodrich of the Iowa State Department of Health for furnishing the data used to accomplish this study.
ACKNOWLEDGMENTS
(Briefs continued next page)
The attending women, possessed of the qualities described, shall instruct her as follows:-"Don't strain when there is no labor pain. For as regards a woman who strains in the absence of labor pains, her efforts are useless, her offspring becomes deformed or diseased or suffers from dyspnea, cough, dehydration and splenic disorders. from: The Caraka Samhita (Ayurvedic medicine) Shree Gulabkunverba Ayurvedil Society Jamnagar, India, 1949
72
AJPH January, 1976, Vol. 66, No. 1
