Chalkley, Martin

Tilley, Colin

English

Objective Recently the issue of access to health services has been brought into sharp focus by clear evidence of rationing patients queuing for NHS registration in the NHS General Dental Services. Conventional estimates suggest that about 50% of adults are registered per annum. This paper demonstrates that these conventional measures of access and utilisation can generate potentially misleading inferences. Design By analysing individual-level claims data from over 35,000 patients over 6 years we are able to: identify the underlying patterns of utilisation that generate the aggregate 50% registration rate; provide more detailed estimates of utilisation and access; and suggest possible determinants of the patterns of utilisation we observe. Setting Primary Care Results In contrast to conventional estimates of access we nd that access to GDS in Scotland is over 80% over 6 years. Moreover, we find that the population is comprised of a relatively large group of patients (30% of the population) who access GDP services at least once a year and a substantial group (19% of the adult population) who access services only once in 6 years. The groups who access services at intermediate frequencies are less numerous. Conclusions Assessing the e¤ectiveness of the public provision of health care services requires accurate information regarding access to those services. This paper sets out a framework for analysing and interpreting longitudinal data to provide information on the extent of access to health care services

University of Dundee Online Publications

                                                              University of DundeeMeasuring access to health services: general dental services in ScotlandChalkley, Martin; Tilley, ColinPublication date:2004Link to publication in Discovery Research PortalCitation for published version (APA):Chalkley, M., & Tilley, C. (2004). Measuring access to health services: general dental services in Scotland.(Dundee Discussion Papers in Economics; No. 163). University of Dundee.General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 19. Mar. 2016                                                     Department of Economic Studies, University of Dundee, Dundee. DD1 4HN   Dundee Discussion Papers in Economics           Measuring Access to Health Services: General Dental Services in Scotland    Martin Chalkley and Colin Tilley                                                                                                                                                                              Working Paper  No. 163 March 2004 ISSN:1473-236X        Measuring access to health services: GeneralDental Services in ScotlandMartin Chalkley, Department of Economic StudiesColin Tilley, Dental Health Services Research Unit15th March 2004AbstractObjective Recently the issue of access to health services has been broughtinto sharp focus by clear evidence of rationing patients queuing for NHS regis-tration in the NHS General Dental Services. Conventional estimates suggestthat about 50% of adults are registered per annum. This paper demonstratesthat these conventional measures of access and utilisation can generate poten-tially misleading inferences.Design By analysing individual-level claims data from over 35,000 patientsover 6 years we are able to: identify the underlying patterns of utilisation thatgenerate the aggregate 50% registration rate; provide more detailed estimatesof utilisation and access; and suggest possible determinants of the patterns ofutilisation we observe.Setting Primary CareResults In contrast to conventional estimates of access we nd that accessto GDS in Scotland is over 80% over 6 years. Moreover, we nd that thepopulation is comprised of a relatively large group of patients (30% of thepopulation) who access GDP services at least once a year and a substantialgroup (19% of the adult population) who access services only once in 6 years.The groups who access services at intermediate frequencies are less numerous.Conclusions Assessing the e¤ectiveness of the public provision of healthcare services requires accurate information regarding access to those services.This paper sets out a framework for analysing and interpreting longitudinaldata to provide information on the extent of access to health care services.11 IntroductionEnsuring access to health services is a key objective of health care policy. Accesswas a central component of both the recent O¢ ce of Fair Trading investigation intopharmacy services in the UK and the new GMS contract [1], [2]. Recently the issueof access has been brought into sharp focus by clear evidence of rationing in the formof patients queuing for NHS registration in the NHS General Dental Services [3].The purpose of this paper is to assess the extent of access to the publicly fundedGeneral Dental Service (GDS) by adults in Scotland. A number of sources indicatethat approximately 50% of the population of Scotland is registered with an NHSdentist at any point in time. This observation does not, however, provide evidenceregarding the extent to which the stock of registered individuals changes over timeand thus the observation of 50% of the population being registered is consistent witha broad range of patterns of access including either the same group of individualsaccessing NHS dental services at least once every year, or a greater proportion of thepopulation accessing services but doing so infrequently. In planning dental servicesand assessing the e¤ectiveness of public provision, it is important to know which ofthe competing possibilities corresponds to the true position.This paper demonstrates that conventional measures of access and utilisationcan generate potentially misleading inferences. Using data on individual patients,observed over a six year period we are able to identify the underlying patterns ofutilisation that generates the aggregate 50% registration rate and thus provide moredetailed estimates of utilisation and access and suggest possible determinants of thepatterns of utilisation we observe.2 MethodIn the context of NHS General Dental Services, contact with a GDP results in aclaim. The source for our data is MIDAS@DHSRU, which is an anonymised datasetcontaining all NHS GDS claims in Scotland. Our analysis is based on a 1% randomsample of patients for whom a claim is recorded at any time during the period January1997 to December 2002. The sample consists of 35,863 patients for whom there area total of 172,552 claims for treatment. Table 1 provides some descriptive statisticsfor this sample.Table 1 shows, for example, that: the average age of a patient claiming for NHSdental treatment is 45; 57% of claims were made on behalf of female patients; and79% of all courses of treatment had at least one diagnosisclaim.2Table 1: MIDAS@DHSRU descriptive statisticsVariable MeanAge 45Male (%) 43Received at least one diagnosis treatment (%) 79Received at least one preventive treatment (%) 0.1Received at least one periodontal treatment (%) 53Received at least one conservative treatment (%) 44Received at least one surgical treatment (%) 9Received at least one prosthetic treatment (%) 9Received at least one orthodontic treatment (%) 1Fee nominal (£ ) 38Exempt (%) 272.1 Conventional estimates of utilisationIn the analysis that follows we adopt a specic measure of utilisation. To conformwith some of the previous empirical literature in this area and in order to ensurecomparability across other data sets the empirical measure of utilisation we adopt isparticipation: whether an individual uses any General Dental Services at least oncein a year.Of the 35,863 patients in the sample Table 2 shows that about 52% participatedin 1997 and about 47% participated in 2002. These gures correspond closely to thesuggestion [4] that approximately 50% of the adult population is registered or receivetreatment at any point in time.Table 2: Aggregate participation rates per annumYear % receiving treatment1997 51.511998 51.341999 50.032000 48.572001 48.142002 46.83While useful in providing cross sectional information on the aggregate use of NHSdental services, Table 2 fails to exploit the underlying individual-level dynamic datathat generates the aggregate data. In particular this table does not reveal whetherthe participants are the same individuals in each time period or an ever changingstock of patients. For example, an observed 50% participation rate is consistent withhalf the population receiving treatment every year and the other half never receiving3any NHS treatment but is also consistent with every individual in the populationreceiving treatment once every two years. In the rst case there may be a substantialaccess problem in that half the population never sees an NHS dentist, whereas in thesecond case there is 100% access to NHS services, albeit at reduced frequency. Fromthe perspective of planning and formulating policy towards the GDS these two casesare clearly substantially di¤erent.In addition to these extreme examples there are a number of other congurationsof individual participation behaviour that may generate an aggregate participationrate of 50%. To discriminate between these congurations, and thus be in a positionto assess the e¤ectiveness of services delivery, longitudinal or panel data are requiredwhich record individualsparticipation histories over a (usually) relatively short timeperiod.2.2 The composition of utilisation using panel dataOur data source MIDAS@DHSRU permits the decomposition of the aggregateparticipation rates from Table 2 into each individual patients pattern of participationover time. Table 3 illustrates the 7 most frequent patterns of participation in theGDS in Scotland over 6 years. A 1in the Patterncolumn indicates that a patientparticipated in that year whilst a 0indicates they did not. Therefore, of the 35,863patients identied over the 6 years of the sample, 5,847 (16.3% of the sample) patientsattended in each of the 6 years. In contrast, 3,125 (8.7%) patients participated in1997 but were not observed in the sample thereafter.Table 3: Patterns of participation in the GDS 1997-2002Frequency % Pattern5847 16.3 1111113125 8.7 1000002301 6.4 0100002239 6.2 0000011745 4.9 0010001655 4.6 0000101554 4.3 00010017397 48.5 Other patterns35863 100Table 3 illustrates that the most frequent pattern of claims accounting for about14% patients in our sample  is for patients to claim at least once every year. Incontrast, the next 6 most frequent patterns of claims accounting for almost 35%4of patients in our sample comprise those patients that receive treatment in onlyone year over the six-year period.1 Thus participation is split between highly regularusersand highly irregularusers.2.3 The frequency of participationThe patterns of participation in Table 3 may be inuenced by a number of determi-nants and will almost certainly vary for a given individual over time. However, inorder to provide some insight into the nature of participation, we consider the fol-lowing simplied model. We assume that there are I +1 groups of individuals withinthe population. We use i = 0; 1; 2; ::; I to indicate a specic group and assume thatgroup i has ni constituent members. For groups i > 0 we assume that each of theseindividuals accesses the services of a GDP every i years whilst for group i = 0; weassume that the individuals never visit a dentist.2 To account for population dynam-ics, we augment the framework to allow for a xed proportion  of the population toexit (death and out-migration) each year, o¤set by xed proportion  entrants (birthsand in-migrants).We are interested in knowing how important each of these groupsis as a percentage of the population and in order to obtain a closed-form solution forthe population groups ni; we assume that  = , which is approximately true for theScottish population. Hence the number of distinct patients observed in year 1 is,N1 = n1 +12n2 +13n3 +14n4 +15n5 +16n6;whilst in the following year the new patients will be comprised of,N2 = n1 + (1  )12n2 +12n2 + (1  )13n3 +13n3 ++(1  )14n4 +14n4 + (1  )15n5 +15n5 + (1  )16n6 +16n6:In subsequent years, account must be taken of both the survival of the births fromprevious years appearing for the rst time (in proportion to their treatment group)to be treated and the exit of those as yet untreated members of infrequent treatmentgroups.1Table 3 reports only the most frequent 7 patterns of participation. All other patterns aresuppressed.2For reasons of exposition, we present our framework as deterministic. It is straightforward toconsider a probabilistic analogue in which individuals in group i attend a dentist with probabilitypi in any given year.5The resulting equations can be summarised as;0BBBBBBBBB@N1N2N3N4N5N61CCCCCCCCCA=0BBBBBBBBB@1 1=2 1=3 1=4 1=5 1=6 1=2 1=3 1=4 1=5 1=6 2 221=3 1=4 1=5 1=6 2 223 32+331=4 1=5 1=6 2 223 32+3344 63+42 41=5 1=6 2 223 32+3344 63+42 455 104+103 52+51=61CCCCCCCCCA0BBBBBBBBB@n1n2n3n4n5n61CCCCCCCCCA:or in matrix notationN =Mn:The solution of these equations can then be obtained fromn =M 1N:We apply this method to data on N derived from our sample and the results, whichexpress the importance of the di¤erent groups of participants as a percentage of thetotal population, are reported in Table 4.Table 4: The frequency of participationParticipation rate Calculated % of Scottish PopulationOnce per year 30.2Once every two years 13.0Once every three years 9.4Once every four years 5.3Once every ve years 7.2Once every six years 16.2Fewer than one visit in six years non-users 18.7Providing that our sample is representative, Table 4 suggests that an estimate ofthe percentage of non-users in Scotland is 18.7% considerably smaller than the oftenassumed 50%. Moreover, this gure overstates the prevalence of NHS non-usersfortwo reasons. First, access to NHS dental services can occur through utilisation of bothcommunity dental (CDS) and hospital dental (HDS) services that are excluded fromthis analysis. Second, data limitations have restricted our period of investigation toa six year period. Hence, individuals who participate at frequencies lower than onceevery six years are under-represented in our data.33The individuals who are being under-represented here are very infrequent users and thus mightusefully be considered a part of the non-user group.62.4 The determinants of participationThe analysis in Section 2.3 is limited by the assumptions we have imposed upon thedeterminants of participation. In particular we have assumed that participation pat-terns are constant over time and are determined exogenously. Clearly this assumptionis unrealistic. Indeed, the existing literature literature suggests a number of possi-ble determinants of participation including health state, demographics, preferences,prices and income [5], [6] .The precise impact of these determinants on the patterns of participation remainto be identied by future research. However, collecting panel data allows the esti-mation of (at least) two other determinants of participation that conventional crosssectional or aggregate data are unable to identify: state dependence and individualheterogeneity. State dependence refers to the impact of participation today uponparticipation tomorrow and is easy to conceptualise within a health context: forexample, preventive treatment today may make participation tomorrow less likely.Individual heterogeneity refers to the extent to which a patients participation ratemay depend upon their specic characteristics such as, for example, their preferencesfor oral health. Our own preliminary, and other [5] [7], research suggests both factorsare large and signicant determinants of patterns of participation.3 ConclusionThe observation of a relatively xed proportion of individuals registered with GDPsdoes not provide reliable information about the extent of access to General DentalServices because of turnover amongst those registered. In this paper we have setout a framework for analysing and interpreting longer run claims data with a view toeliciting information upon overall utilisation and the pattern of access to GDP servicesin Scotland. This information may be used to assist in planning dental services andassessing the e¤ectiveness of public provision.We nd that, whereas only approximately 50% of the adult population is registeredat any point in time, a much larger percentage of the population close to 80% hashad access to GDP services over a six year period. Our framework permits a moredetailed breakdown of the pattern of access than that previously available. We ndthat the population is comprised of a relatively large group of individuals (30% of theadult population) who access GDP services at least once per year and a substantialgroup (19% of the adult population) who access services only once in six years. Thegroups within the population who access services at intermediate frequencies are less7numerous. These observations would appear to have important implications for policyreform and beg questions regarding the likely impact of changes in patient charges,changes in the frequency of dental recall, changes in service availability and changesin GDP contracts for the overall impact of GDP services. Finally, whilst we haveidentied a number of the potential determinants of participation rates, the impactof these determinants and whether the pattern of participation we observe is optimalin the sense that it is either cost-e¤ective or equitable remain questions for furtherresearch.References[1] OFT (O¢ ce of Fair Trading). The control of entry regulations and retail pharmacyservices in the UK: A report of an OFT market investigation. January 2003,London.[2] NHS Confederation. Investing in General Practice  The New General MedicalServices Contract. February 2003. London.[3] The Guardian. Half of Britain has no dentist. Wednesday February 18, 2004.(http://society.guardian.co.uk/primarycare/story/0,8150,1151018,00.html).[4] Scottish Executive Health Department. An Action Plan for Dental Services inScotland. August 2000. Edinburgh.[5] Propper C.The Demand for Private Health Care in the UK. Journal of HealthEconomics 2000; 19: 855-76.[6] Carr-Hill RA, Rice N, Roland M. Socioeconomic determinats of rates of consul-tation in general practice based on the fourth national mobidity survey of generalpractices. British Medical Journal 1996. 312: 1008-1012.[7] Jordan K, Ong BN, Croft P. Previous consultation and self reported health statuisas predictors of future demand for primary care. Journal of Epidemiology andpublic Health 2003; 57: 109-113.8

ce of Fair Trading). The control of entry regulations and retail pharmacy services in the UK: A report of an OFT market investigation.

Half of Britain has no dentist.

Investing in General Practice  The New General Medical Services Contract.

Previous consultation and self reported health statuis as predictors of future demand for primary care.

Propper C.The Demand for Private Health Care in the UK.

Scottish Executive Health Department. An Action Plan for Dental Services in Scotland.

Socioeconomic determinats of rates of consultation in general practice based on the fourth national mobidity survey of general practices.

Dundee Discussion Papers in Economics 163:Measuring access to health services: general dental services in Scotland

                                                                    University of DundeeDundee Discussion Papers in Economics 163Chalkley, Martin; Tilley, ColinPublication date:2004Link to publication in Discovery Research PortalCitation for published version (APA):Chalkley, M., & Tilley, C. (2004). Dundee Discussion Papers in Economics 163: Measuring access to healthservices: general dental services in Scotland. (Dundee Discussion Papers in Economics; No. 163). University ofDundee.General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or othercopyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated withthese rights. • Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain. • You may freely distribute the URL identifying the publication in the public portal.Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 30. Jul. 2023                                                     Department of Economic Studies, University of Dundee, Dundee. DD1 4HN   Dundee Discussion Papers in Economics           Measuring Access to Health Services: General Dental Services in Scotland    Martin Chalkley and Colin Tilley                                                                                                                                                                              Working Paper  No. 163 March 2004 ISSN:1473-236X        Measuring access to health services: GeneralDental Services in ScotlandMartin Chalkley, Department of Economic StudiesColin Tilley, Dental Health Services Research Unit15th March 2004AbstractObjective Recently the issue of access to health services has been broughtinto sharp focus by clear evidence of rationing patients queuing for NHS regis-tration in the NHS General Dental Services. Conventional estimates suggestthat about 50% of adults are registered per annum. This paper demonstratesthat these conventional measures of access and utilisation can generate poten-tially misleading inferences.Design By analysing individual-level claims data from over 35,000 patientsover 6 years we are able to: identify the underlying patterns of utilisation thatgenerate the aggregate 50% registration rate; provide more detailed estimatesof utilisation and access; and suggest possible determinants of the patterns ofutilisation we observe.Setting Primary CareResults In contrast to conventional estimates of access we nd that accessto GDS in Scotland is over 80% over 6 years. Moreover, we nd that thepopulation is comprised of a relatively large group of patients (30% of thepopulation) who access GDP services at least once a year and a substantialgroup (19% of the adult population) who access services only once in 6 years.The groups who access services at intermediate frequencies are less numerous.Conclusions Assessing the e¤ectiveness of the public provision of healthcare services requires accurate information regarding access to those services.This paper sets out a framework for analysing and interpreting longitudinaldata to provide information on the extent of access to health care services.11 IntroductionEnsuring access to health services is a key objective of health care policy. Accesswas a central component of both the recent O¢ ce of Fair Trading investigation intopharmacy services in the UK and the new GMS contract [1], [2]. Recently the issueof access has been brought into sharp focus by clear evidence of rationing in the formof patients queuing for NHS registration in the NHS General Dental Services [3].The purpose of this paper is to assess the extent of access to the publicly fundedGeneral Dental Service (GDS) by adults in Scotland. A number of sources indicatethat approximately 50% of the population of Scotland is registered with an NHSdentist at any point in time. This observation does not, however, provide evidenceregarding the extent to which the stock of registered individuals changes over timeand thus the observation of 50% of the population being registered is consistent witha broad range of patterns of access including either the same group of individualsaccessing NHS dental services at least once every year, or a greater proportion of thepopulation accessing services but doing so infrequently. In planning dental servicesand assessing the e¤ectiveness of public provision, it is important to know which ofthe competing possibilities corresponds to the true position.This paper demonstrates that conventional measures of access and utilisationcan generate potentially misleading inferences. Using data on individual patients,observed over a six year period we are able to identify the underlying patterns ofutilisation that generates the aggregate 50% registration rate and thus provide moredetailed estimates of utilisation and access and suggest possible determinants of thepatterns of utilisation we observe.2 MethodIn the context of NHS General Dental Services, contact with a GDP results in aclaim. The source for our data is MIDAS@DHSRU, which is an anonymised datasetcontaining all NHS GDS claims in Scotland. Our analysis is based on a 1% randomsample of patients for whom a claim is recorded at any time during the period January1997 to December 2002. The sample consists of 35,863 patients for whom there area total of 172,552 claims for treatment. Table 1 provides some descriptive statisticsfor this sample.Table 1 shows, for example, that: the average age of a patient claiming for NHSdental treatment is 45; 57% of claims were made on behalf of female patients; and79% of all courses of treatment had at least one diagnosisclaim.2Table 1: MIDAS@DHSRU descriptive statisticsVariable MeanAge 45Male (%) 43Received at least one diagnosis treatment (%) 79Received at least one preventive treatment (%) 0.1Received at least one periodontal treatment (%) 53Received at least one conservative treatment (%) 44Received at least one surgical treatment (%) 9Received at least one prosthetic treatment (%) 9Received at least one orthodontic treatment (%) 1Fee nominal (£ ) 38Exempt (%) 272.1 Conventional estimates of utilisationIn the analysis that follows we adopt a specic measure of utilisation. To conformwith some of the previous empirical literature in this area and in order to ensurecomparability across other data sets the empirical measure of utilisation we adopt isparticipation: whether an individual uses any General Dental Services at least oncein a year.Of the 35,863 patients in the sample Table 2 shows that about 52% participatedin 1997 and about 47% participated in 2002. These gures correspond closely to thesuggestion [4] that approximately 50% of the adult population is registered or receivetreatment at any point in time.Table 2: Aggregate participation rates per annumYear % receiving treatment1997 51.511998 51.341999 50.032000 48.572001 48.142002 46.83While useful in providing cross sectional information on the aggregate use of NHSdental services, Table 2 fails to exploit the underlying individual-level dynamic datathat generates the aggregate data. In particular this table does not reveal whetherthe participants are the same individuals in each time period or an ever changingstock of patients. For example, an observed 50% participation rate is consistent withhalf the population receiving treatment every year and the other half never receiving3any NHS treatment but is also consistent with every individual in the populationreceiving treatment once every two years. In the rst case there may be a substantialaccess problem in that half the population never sees an NHS dentist, whereas in thesecond case there is 100% access to NHS services, albeit at reduced frequency. Fromthe perspective of planning and formulating policy towards the GDS these two casesare clearly substantially di¤erent.In addition to these extreme examples there are a number of other congurationsof individual participation behaviour that may generate an aggregate participationrate of 50%. To discriminate between these congurations, and thus be in a positionto assess the e¤ectiveness of services delivery, longitudinal or panel data are requiredwhich record individualsparticipation histories over a (usually) relatively short timeperiod.2.2 The composition of utilisation using panel dataOur data source MIDAS@DHSRU permits the decomposition of the aggregateparticipation rates from Table 2 into each individual patients pattern of participationover time. Table 3 illustrates the 7 most frequent patterns of participation in theGDS in Scotland over 6 years. A 1in the Patterncolumn indicates that a patientparticipated in that year whilst a 0indicates they did not. Therefore, of the 35,863patients identied over the 6 years of the sample, 5,847 (16.3% of the sample) patientsattended in each of the 6 years. In contrast, 3,125 (8.7%) patients participated in1997 but were not observed in the sample thereafter.Table 3: Patterns of participation in the GDS 1997-2002Frequency % Pattern5847 16.3 1111113125 8.7 1000002301 6.4 0100002239 6.2 0000011745 4.9 0010001655 4.6 0000101554 4.3 00010017397 48.5 Other patterns35863 100Table 3 illustrates that the most frequent pattern of claims accounting for about14% patients in our sample  is for patients to claim at least once every year. Incontrast, the next 6 most frequent patterns of claims accounting for almost 35%4of patients in our sample comprise those patients that receive treatment in onlyone year over the six-year period.1 Thus participation is split between highly regularusersand highly irregularusers.2.3 The frequency of participationThe patterns of participation in Table 3 may be inuenced by a number of determi-nants and will almost certainly vary for a given individual over time. However, inorder to provide some insight into the nature of participation, we consider the fol-lowing simplied model. We assume that there are I +1 groups of individuals withinthe population. We use i = 0; 1; 2; ::; I to indicate a specic group and assume thatgroup i has ni constituent members. For groups i > 0 we assume that each of theseindividuals accesses the services of a GDP every i years whilst for group i = 0; weassume that the individuals never visit a dentist.2 To account for population dynam-ics, we augment the framework to allow for a xed proportion  of the population toexit (death and out-migration) each year, o¤set by xed proportion  entrants (birthsand in-migrants).We are interested in knowing how important each of these groupsis as a percentage of the population and in order to obtain a closed-form solution forthe population groups ni; we assume that  = , which is approximately true for theScottish population. Hence the number of distinct patients observed in year 1 is,N1 = n1 +12n2 +13n3 +14n4 +15n5 +16n6;whilst in the following year the new patients will be comprised of,N2 = n1 + (1  )12n2 +12n2 + (1  )13n3 +13n3 ++(1  )14n4 +14n4 + (1  )15n5 +15n5 + (1  )16n6 +16n6:In subsequent years, account must be taken of both the survival of the births fromprevious years appearing for the rst time (in proportion to their treatment group)to be treated and the exit of those as yet untreated members of infrequent treatmentgroups.1Table 3 reports only the most frequent 7 patterns of participation. All other patterns aresuppressed.2For reasons of exposition, we present our framework as deterministic. It is straightforward toconsider a probabilistic analogue in which individuals in group i attend a dentist with probabilitypi in any given year.5The resulting equations can be summarised as;0BBBBBBBBB@N1N2N3N4N5N61CCCCCCCCCA=0BBBBBBBBB@1 1=2 1=3 1=4 1=5 1=6 1=2 1=3 1=4 1=5 1=6 2 221=3 1=4 1=5 1=6 2 223 32+331=4 1=5 1=6 2 223 32+3344 63+42 41=5 1=6 2 223 32+3344 63+42 455 104+103 52+51=61CCCCCCCCCA0BBBBBBBBB@n1n2n3n4n5n61CCCCCCCCCA:or in matrix notationN =Mn:The solution of these equations can then be obtained fromn =M 1N:We apply this method to data on N derived from our sample and the results, whichexpress the importance of the di¤erent groups of participants as a percentage of thetotal population, are reported in Table 4.Table 4: The frequency of participationParticipation rate Calculated % of Scottish PopulationOnce per year 30.2Once every two years 13.0Once every three years 9.4Once every four years 5.3Once every ve years 7.2Once every six years 16.2Fewer than one visit in six years non-users 18.7Providing that our sample is representative, Table 4 suggests that an estimate ofthe percentage of non-users in Scotland is 18.7% considerably smaller than the oftenassumed 50%. Moreover, this gure overstates the prevalence of NHS non-usersfortwo reasons. First, access to NHS dental services can occur through utilisation of bothcommunity dental (CDS) and hospital dental (HDS) services that are excluded fromthis analysis. Second, data limitations have restricted our period of investigation toa six year period. Hence, individuals who participate at frequencies lower than onceevery six years are under-represented in our data.33The individuals who are being under-represented here are very infrequent users and thus mightusefully be considered a part of the non-user group.62.4 The determinants of participationThe analysis in Section 2.3 is limited by the assumptions we have imposed upon thedeterminants of participation. In particular we have assumed that participation pat-terns are constant over time and are determined exogenously. Clearly this assumptionis unrealistic. Indeed, the existing literature literature suggests a number of possi-ble determinants of participation including health state, demographics, preferences,prices and income [5], [6] .The precise impact of these determinants on the patterns of participation remainto be identied by future research. However, collecting panel data allows the esti-mation of (at least) two other determinants of participation that conventional crosssectional or aggregate data are unable to identify: state dependence and individualheterogeneity. State dependence refers to the impact of participation today uponparticipation tomorrow and is easy to conceptualise within a health context: forexample, preventive treatment today may make participation tomorrow less likely.Individual heterogeneity refers to the extent to which a patients participation ratemay depend upon their specic characteristics such as, for example, their preferencesfor oral health. Our own preliminary, and other [5] [7], research suggests both factorsare large and signicant determinants of patterns of participation.3 ConclusionThe observation of a relatively xed proportion of individuals registered with GDPsdoes not provide reliable information about the extent of access to General DentalServices because of turnover amongst those registered. In this paper we have setout a framework for analysing and interpreting longer run claims data with a view toeliciting information upon overall utilisation and the pattern of access to GDP servicesin Scotland. This information may be used to assist in planning dental services andassessing the e¤ectiveness of public provision.We nd that, whereas only approximately 50% of the adult population is registeredat any point in time, a much larger percentage of the population close to 80% hashad access to GDP services over a six year period. Our framework permits a moredetailed breakdown of the pattern of access than that previously available. We ndthat the population is comprised of a relatively large group of individuals (30% of theadult population) who access GDP services at least once per year and a substantialgroup (19% of the adult population) who access services only once in six years. Thegroups within the population who access services at intermediate frequencies are less7numerous. These observations would appear to have important implications for policyreform and beg questions regarding the likely impact of changes in patient charges,changes in the frequency of dental recall, changes in service availability and changesin GDP contracts for the overall impact of GDP services. Finally, whilst we haveidentied a number of the potential determinants of participation rates, the impactof these determinants and whether the pattern of participation we observe is optimalin the sense that it is either cost-e¤ective or equitable remain questions for furtherresearch.References[1] OFT (O¢ ce of Fair Trading). The control of entry regulations and retail pharmacyservices in the UK: A report of an OFT market investigation. January 2003,London.[2] NHS Confederation. Investing in General Practice  The New General MedicalServices Contract. February 2003. London.[3] The Guardian. Half of Britain has no dentist. Wednesday February 18, 2004.(http://society.guardian.co.uk/primarycare/story/0,8150,1151018,00.html).[4] Scottish Executive Health Department. An Action Plan for Dental Services inScotland. August 2000. Edinburgh.[5] Propper C.The Demand for Private Health Care in the UK. Journal of HealthEconomics 2000; 19: 855-76.[6] Carr-Hill RA, Rice N, Roland M. Socioeconomic determinats of rates of consul-tation in general practice based on the fourth national mobidity survey of generalpractices. British Medical Journal 1996. 312: 1008-1012.[7] Jordan K, Ong BN, Croft P. Previous consultation and self reported health statuisas predictors of future demand for primary care. Journal of Epidemiology andpublic Health 2003; 57: 109-113.8

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Dundee Discussion Papers in Economics 163:Measuring access to health services: general dental services in Scotland

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