Diabetes mellitus is a major cause of morbidity and

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1 EUROPEAN JOURNAL OF PUBLIC HEALTH 199S; S: The prevlence of dibetes mellitus in the Netherlnds A quntittive review CAROLINE A. BAAN, LUC BONNEUX, DIRK RUWAARD, EDITH J.M. FESKENS * The prevlence of dibetes bove the ge of 30 yers in The Netherlnds ws estimted nd the influence of methodologicl vribles on the reported prevlence rtes ws quntified. Fifteen Dutch studies performed since 1970 were entered in logistic regression models with the presence or bsence of known dibetes bove the ge of 30 yers s dependent vrible. In order to quntify the vribility mong studies, the study methodology nd popultion chrcteristics were chosen s independent vribles. The ge-stndrdized prevlence of known dibetes vried between the studies. The totl prevlence of known dibetes bove the ge of 30 yers in 1993 cn be estimted t 2.7% on the bsis of the cses reported by generl prctitioners nd t 3.2% bsed on self-reported cses in surveys. The prevlence ccording to ge incresed by 7.1% per life yer for men nd by 7.7% for women. These ssocitions were essentilly similr in ll studies. Systemtic screening, performed with n orl glucose tolernce test, reveled prevlence which ws times higher.depending on the method used, the number of subjects with known dibetes in the Netherlnds in 1993 vried between 235,000 nd 285,000. After systemtic screening, this prevlence will be times higher. These estimtes my serve vrious gols. The prevlence rtes bsed on self-reports or reports by generl prctitioners re importnt for estimting helth cre use. Prevlence rtes bsed on screening re relevnt for preventive strtegies nd ltent helth cre needs. Dibetes mellitus is mjor cuse of morbidity nd mortlity in the world. Non-insulin-dependent dibetes mellitus (N1DDM) is by fr the most common form nd thus cuses the most co-morbidity.' 1^ As prevlence increses shrply with ge, it is n importnt determinnt of helth cre needs in n geing society. To ssess future needs for helth cre, policy mkers need more informtion on the number of ptients nd chnges in prevlence over time. This requires relible estimtes of ge- nd sex-specific prevlence rtes. However, prevlence studies re hrd to interpret. Reported prevlence rtes my vry due to vrious popultion chrcteristics or differences in methodology. Popultions my vry by composition (ge nd sex) or by other chrcteristics such s obesity nd other determinnts of dibetes. Methodologicl diversity is cused by selection of the study popultion, cse definition nd cse scertinment. The study popultion my, for instnce, be rndom smple of the * C.A. Bn u, L Bonneux 1. D. Ruwrd 2, E.J.M. Feskens 3 1 Deprtment of Public Helth, Ersmus University Rotterdm, Rotterdm, The Netherlnds 2 Deprtment for Public Helth Forecsting, Ntionl Institute of Public Helth nd the Environment. Bilthoven, The Netherlnds 3 Deprtment for Chronic Disese nd Environmentl Epidemiology, Ntionl Institute of Public Helth nd the Environment, Bilthoven, The Netherlnds Correspondence: Croline A. Bn, MSc, Deprtment of Public Helth, Ersmus University Rotterdm, P.O. Box 1738, 3000 DR Rotterdm, The Netherlnds, tel , fx , e-mil: bn@mgz.fgg.eur.nl Key words: dibetes mellitus, pooled nlysis, prevlence generl popultion (survey) or hve been selected on the bsis of helth cre use (popultion in generl prctice). Cse definitions hve chnged over time. In 1965, dignostic criteri were first formulted by the World Helth Orgniztion (WHO) nd revised nd stndrdized in 1980 nd ' 4 Moreover, cses cn be scertined from self-reports, generl prctitioners reports or by screening with n orl glucose tolernce test (OGTT). Obviously, systemtic screening for n often symptomtic disese will yield much higher prevlence rtes. To obtin best possible estimte of the prevlence of dibetes in the dult popultion in The Netherlnds, we compred ll the studies performed since 1970 nd tried to ccount for differences in methodologicl chrcteristics by using logistic regression models. The estimted prevlence rtes will be judged ccording to their relevnce to helth policy. METHODS Dt sources The dt were collected from ll studies conducted since 1970 on the prevlence of dibetes mellitus in the dult popultion in The Netherlnds. Few were published in peer reviewed ppers nd most were identified through the snowbll method (checking references in ll the publictions found) nd expert dvice. We turned up 22 studies reporting the prevlence of dibetes mellitus in The Netherlnds. For inclusion in our nlyses, the studies were required to report, for men nd women Downloded from by guest on 30 November 2018

2 Prevlence of dibetes melhtus seprtely, ge-specific prevlences for ge groups which differed by mximum of 20 yers. This excluded five studies. 5 " 9 One study ws excluded from nlysis becuse of its highly selective study popultion (ptients in nursing homes nd homes for the elderly). 10. Another study ws excluded from nlysis becuse ll the dibetic ptients who visited the generl prctitioner were registered during three month period. This period ws too short to estimte the prevlence of dibetes relibly. 11 Fifteen studies qulified for nlysis. Tble I gives n overview of the chrcteristics of these studies. They were performed either in generl prctices or s surveys. Cses of known dibetic ptients were scertined by mens of reports from generl prctitioners or self-reports in questionnire. Two studies mesured the prevlence of dibetes t severl points in time. 12 ' 13 Four studies identified, next to ll known cses of dibetes, unknown cses of dibetes by systemtic screening of the remining popultion with n OGTT. These four studies differed from ech other in type of OGTT (fsting or non-fsting) nd study popultion (survey or popultion from generl prctice). 14 ' 24 " 26 Anlyses of prevlence The dt were nlysed using logistic regression model with the presence or bsence of dibetes mellitus s dependent vrible. The sme method ws used for estimting the prevlence of hypertension on the bsis of number of studies. 27 The sttisticl pckge EGRET ws used in ll the nlyses. We restricted the nlyses to ges 30 yers nd bove. All the nlyses were performed for men nd women seprtely. Age ws lwys specified s n independent vrible; the medin ge of ech ge group ws used. When open-ended, ge groups were excluded from the nlyses, s the medin ge in such open-ended ge groups my differ strongly between studies. The numbers in ech ge nd sex group were used s weights. Two studies ' reported only ggregted smple sizes. However the distribution by ge nd sex of these studies ws equl to the Dutch popultion during dit period, which mde it possible to clculte the number in ech ge nd sex group. In the first nlysis, the study ws chosen s n independent (dummy) vribles in order to identify the differences between the studies, djusted for different ge structures. The Sentinel Sttion study performed in ws tken s reference, becuse this study hs the lrgest smple size. Becuse four studies lso mesured symptomtic dibetes by screening with n OGTT, we performed the nlysis twice. First, the reported prevlence rtes of known dibetes were entered s dependent vrible in the model, while for the second nlysis for these four studies 14 ' 24 ~ 26 we used the sum of known nd newly dignosed dibetes. Next, we tried to find n explntion for the difference in the prevlence rtes of known dibetes between studies by estimting the influence of methodologicl vrition on the prevlence of dibetes. Report by generl prctitioner nd self-report in survey were chosen s independent vribles, djusted for ge nd clendr yer. Becuse the four studies using n OGTT used different test nd methodology, pooled estimte of the effect of systemtic screening on the prevlence rte could not be clculted. The regression equtions, used for the two nlyses re given in the ppendix. The coefficients from the logistic regression models were used to estimte the prevlence of dibetes in The Netherlnds. Tble 1 Chrcteristics of the 15 studies on the prevlence of dibetes mellitus in The Netherlnds used in the nlysis Nme of the study Generl prctice (GP) Survey Sentinel Sttion CMR-Nijmegen' 3 Twello Study 14 Autonomy Project Trnsition Project Heerde study EPOZ 18 LSO 19 CFRM 20 Helth Survey 21 GLOBE 22 LASA 23 Hoom Study 24 Zutphen Study Rotterdm Study Period Smple size 162,626 12, ,163 40,796 11,800 10,616 7,968 36,000 41,450 18,973 3,108 2, ,983 Age (yers) O->65 0->80 O-> > O->75 0-> >85 CMR: Continuous Morbidity Registrtion EPOZ: Epidemiologic Preventive Reserch Zoetermeer LSG Living-Sitution Study CFRM: Crdiovsculr Risk Fctors Monitonngs Project GLOBE: Helth nd Living Conditions of the popultion of Eindhoven nd surroundings LASA: Longitudinl Ageing Study Amsterdm OGTT: orl glucose tolernce test Cse scertinment nd fsting OGTT nd fsting OGTT nd fsting OGTT nd non-fsting OGTT Downloded from by guest on 30 November 2018

3 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 3 RESULTS The surveys reported higher prevlences s compred with the Sentinel Sttion, with the exception of the Epidemiologic Preventive Reserch Zoetermeer (EPOZ) study (tble 2). Within the studies performed in generl prctice, the Continuous Morbidity Registrtion (CMR)- Nijmegen nd the Twello study reported significnt higher prevlences thn the reference study. The two studies which mesured the prevlence t severl points in time 12 ' 13 showed contrdictory results. The Sentinel Sttions reported lower prevlence in s compred with CMR-Nijmegen study showed slight increse in prevlence over time, for both men nd women. The four studies which identified unknown cses of dibetes in ddition to ll known cses of dibetes by systemticlly screening the remining popultion with n OGTT, reported higher prevlence estimtes compred with the studies identifying only the known cses of dibetes. The number of known dibetic ptients could be seprted from the newly dignosed ptients in these studies, enbling us to compre the prevlence estimtes of known versus known nd newly dignosed within the four studies. Three of the four studies reported prevlences times s high s their own prevlence rte of known dibetes. The fourth study 1 '' reported prevlences six times s high s its own prevlence rte of known dibetes nd cn be considered s n outlier. Some of the differences between the studies my be explined by methodologicl vrition. Mesuring known dibetes in survey using self-reported cses resulted in higher prevlence rtes thn those bsed on reports mde by generl prctitioners (tble 3). These differences were somewht lrger for men thn for women but did not differ significntly: n odds rtio of 1.47 (95% CI: ) for men versus 1.14 (95% CI: ) for women. The prevlence of known dibetes mellitus incresed for men by 7.1% (95% CI: ) for ech yer of ge nd by 7.7% (95% CI: ) for women. When estimting the increse in prevlence by ge for ech of the studies seprtely, we found tht the pooled estimte of the increse by ge fell within the confidence Tble 2 Vrition in the prevlence of dibetes mellitus in The Netherlnds expressed s odds rtios (95% confidence intervls) djusted for ge Vrible Generl prctice Survey Sentinl Sttion CMR-Nijmegen Twello Study Autonomy Study Trnsition Study Heerde Study EPOZ LSO CFRM Helth Survey GLOBE LASA Hoom Study Zutphen Study Rotterdm Study Period Men 0.82 ( ) 1.19 ( ) 1.43( ) 1.56( ) 1.48( ) 1.48( ) 1.76 ( ) 0.93 ( ) 1.04( ) 1.12( ) 0.83 ( ) 1.23 ( ) 1.32( ) 1.30( ) 1.71 ( ) 1.39( ) 1.05 ( ) 1.59( ) 2.08( ) Known dibetes Women 0.74 ( ) 1.08 ( ) 1.22( ) 1.27(-1.62) 1.33( ) 1.44( ) 1.70( ) 1.04( ) 0.97( ) 1.08( ) 0.74 ( ) 1.15 ( ) 0.92 ( ) 1.11 ( ) 1.17( ) 1.05 ( ) 0.98( ) ( ) Known nd newly dignosed dibetes Men 7.08 ( ) 2.93 ( ) 3.10( ) 2.84 ( ) Women 5.59 ( ) 2.32( ) ( ) Downloded from by guest on 30 November 2018 : No newly dignosed dibetes vilble Tble 3 Influence of methodologicl vrition on the reported prevlence estimtes expressed s odds rtios (95% confidence intervls) djusted for ge nd clender yer Vrible Age (continuous) Clender yer (continuous) in survey versus report by GP Men ( ) ( ) ( ) Women ( ) 0.99 (0.98-) 1.14 ( )

4 Prevlence of dibetes mellitus Prevlence (%) Prevlence (%) o o ' ' Age Figure 1 Prevlence of dibetes for men ccording to survey with self-reported dt ( ) or report by generl prctitioner ( ). The study prevlences re plotted with the size of the bll s n indictor for the smple size. Figure 2 Prevlence of dibetes for women ccording to survey with self-reported dt ( ) or report by generl prctitioner ( ). The study prevlences re plotted with the size of the bll s n indictor for the smple size. intervls of ech individul study (dt not shown). No effect of clender yer could be observed. The coefficients estimted from the logistic model were used to estimte the prevlence of known dibetes in The Netherlnds in 1993 (figures I nd 2). The best possible estimte of the ge-specific prevlence vried with the methodology used. In The Netherlnds, the totl number of dibetic ptients bove the ge of 30 yers in 1993 ws 235,000 (2.7%) bsed on cses reported by generl prctitioners nd 285,000 (3.2%) bsed on self-reported cses in survey. The prevlence is higher for women of ll ges. Systemtic screening with n OGTT will yield prevlence rtes times s high. Assuming this increse in the prevlence rte is similr in ll ge groups, the totl number of subjects with dibetes fter systemtic screening of the totl popultion will mount to 460,000 (5.2%) bsed on the reports of generl prctitioners or 560,000 (6.4%) bsed on self-reports in survey. These estimtes should be interpreted s n upper limit, s they re bsed on systemtic screening with single glucose tolernce test. The use of repeted mesurements will result in lower prevlence of dibetes.28 into the effect of methodologicl vritions on the estimtes of the prevlence of dibetes. Obviously, the results need to be interpreted with cution, but it is lso importnt to relize tht the studies re not heterogeneous in ll spects. For instnce, the prevlence increse by ge, estimted from the pooled nlysis, ws more or less similr in ll studies. The nlyses strted from ge 30 yers. The incidence nd prevlence of NIDDM re by fr the gretest29'-5^ older ges. Almost 85% of ll dibetic ptients, registered in 19 generl prctices, hs the insulin-dependent form of dibetes. The percentge of insulin-dependent dibetes (1DDM) ptients dignosed before ge 30 yers, but who were older thn 30 yers when the studies were crried out, is expected to be low nd decreses with ge. In the Heerde study in which discrimintion could be mde between NIDDM nd IDDM bsed on ge of dignosis nd tretment with insulin, the percentge of IDDM ptients decresed from 30% t ge 30 yers to less thn 10% t ge 80 yers.17 Therefore, the results of our nlyses minly concern NIDDM ptients. A chnging cse definition over time is mjor problem in the interprettion of the different studies nd in the interprettion of time series.as the definition becomes more nd more specific, it my be ssumed tht the number of wrongly clssified cses will drop nd tht, moreover, the prevlence of dibetes ws reltively overestimted in the pst. Prt of the differences in prevlence rtes observed between the studies might be explined by these chnges in cse definition. In severl studies it ws checked whether the dignostic criteri hd chnged nd how this might hve influenced the prevlences reported. 17>-52The effect of chnged criteri on the reported prevlence differed mong these studies. The CMRNijmegen study reported tht 13% of the dibetic ptients did not hve dibetes ccording to the WHO criteri of Moreover, the CMR-Nijmegen study lso reported tht for 14% of the subjects, the dignostic criteri could not be trced nymore.-52 The Heerde study found tht in 12.8% of the previously dignosed dibetic ptients the I DISCUSSION We evluted ll the studies published in The Netherlnds in order to obtin tenttive estimte of the prevlence of dibetes. The ge-stndrdized prevlence of known dibetes vried considerbly mong the studies, with higher prevlence in surveys using self-reported dt. The prevlence increse by ge is cler-cut. When systemtic screening with n OGTT ws performed, the prevlence rtes were times higher. Pooling the dt from heterogeneous studies to rrive t single estimte might be considered scientificlly unsound undertking. However, it seemed the only wy to overcome the shortcomings of ech individul study nd to minimize the loss of informtion. If only selected dt sources re considered, the selection might be guided by the (often unconscious) wishes of the reviewer nd yield bised results. Furthermore, pooling offers n insight Downloded from by guest on 30 November 2018 Age /

5 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 3 dignosis could not be reconfirmed with n OGTT when the WHO criteri of 1985 were pplied. In generl, ptients dignosed by single glucose tolernce test nd/or treted with diet were shown to be non-dibetic ccording to the WHO criteri of For the surveys which used self-reported dt, it is impossible to judge if nd how cse definition influenced the reported prevlence. In studies using screening with n OGTT, newly dignosed dibetes ws defined ccording to the WHO criteri of Another explntion for the observed differences in the prevlence rtes between the studies could be the differences in the previling interest of generl prctitioners in NIDDM. Since the presence of NIDDM is not lwys cliniclly mnifest, some of the subjects with dibetes re undignosed s such. 33 ' 34 Some generl prctitioners will be more wre of this phenomon nd my be more ttentive to dignosing dibetes. Surveys using self-reported dt resulted in higher prevlence estimtes s compred with those bsed on reports mde by generl prctitioners. A possible explntion is tht those responding to survey my stte tht they re dibetic but re no longer registered in generl prctice s dibetic ptients (becuse of, for exmple, chnged dignostic criteri or repeted mesurements). On the other hnd, in registering the cses in generl prctice dibetic ptients cn be missed due to dministrtion problems (hospitl visits fil to be reported to the generl prctitioner) or the pproch to registrtion (only ptients who visit the generl prctitioner in certin period re counted). 35 In prticulr, those ptients who re treted with diet only my cuse discrepncy between selfreported dt nd those reported by generl prctitioners. As neither the generl prctitioners nor the surveys took into ccount persons who re institutionlized in nursing homes or rest homes (only the Longitudinl Ageing Study Amsterdm (LASA) included the institutionlized popultion) underestimtion of the prevlence is likely. A study in nursing homes nd rest-homes, which ws excluded from our nlysis for resons of comprbility, reported higher prevlence of dibetes thn the estimted prevlences of our nlysis: 13% (95% CI: 10-16) for men ged yers nd 21% (95% CI: 19-23) for women of this ge, compred with our estimted prevlences of 5.7 nd 8.4% for men nd women respectively. In The Netherlnds, 4.3% of ll men nd 7.9% of ll women ged yers re institutionlized. 10 Compring the prevlence estimtes with other countries, The Netherlnds ppers to be low in the hierrchy. In other Europen countries, surveys revel n ge-djusted prevlence of known dibetes between 30 nd 64 yers of ge which vries from 1.8% in Russi to 10.7% in Itly. 1 In Americn surveys, the ge-stndrdized prevlences of known dibetes in the White popultion vries between 3 nd 8% This is comprble to our estimte of known dibetes of 1.7% between the ges of 30 nd 64 yers. The effect of systemtic screening on the prevlence rtes cn best be estimted by compring studies mesuring known nd unknown dibetes. Three studies which systemticlly screened for unknown dibetes reported times higher prevlence estimtes. 24 ~ 26 The Twello study reported prevlence rtes 6 times s high nd is considered to be n outlier. Although it is uncler why this study reported such extreme prevlence rtes, few comments re in order. The study popultion of this study ws reltively smll (n=560) nd ws bsed on generl prctice in rurl villge. The lmost doubled prevlence found when systemtic screening with n OGTT ws crried out corresponds with studies which found tht pproximtely 50% or more of the subjects with NIDDM re undignosed. ' 4 The three screening studies used single glucose tolernce test, which is known to be prone to intr individul vrition. 36 ' 37 This my explin prt of the different prevlence estimtes mong the four studies using n OGTT. The Hoorn Study ssessed the prevlence of dibetes in smple using two OGTTs, repeted during period of 2-6 weeks. The prevlence of newly dignosed dibetes fter two OGTTs ws lower compred with single test (3.4 versus 4.3%), probbly due to regression towrds the men. 28 Repeted mesurements re dvisble to void possible misclssifiction nd to obtin more vlid estimte of the prevlence of dibetes. In our nlysis, we included studies conducted in the period However, trends in time were difficult to interpret. As noted before, cse definitions becme more specific, inducing n rtificil decrese by minimizing flse positives. The two studies which mesured prevlence t severl points in time were contrdictory. The Sentinel Sttion showed decrese in prevlence, but only mesured the dibetes the prevlence t two points in time. The decresed prevlence is probbly due to clernce of the dibetic register in generl prctice. The only study with continuous registrtion of dibetes since 1970, the CMR-Nijmegen study, showed slight increse in prevlence. However, these estimtes were bsed on smll numbers. In other popultions too, little is known bout seculr time trends. Two studies reported n increse in prevlence in the US over the pst decdes. 39 ' 40 This issue lso merits further study in The Netherlnds. In this study, the prevlence of known dibetes incresed for men by 7.1% for ech yer of ge nd by 7.7% for women. Age ppers to be relible predictor for the future numbers of ptients in n geing society. The number of ptients ged 30 yers nd up will increse by 36% (95% CI: 19-41%) between 1993 nd 2010 bsed on ge-specific prevlence rtes. For helth policy mkers, it is importnt to relize tht, depending on the wy prevlence rtes re mesured, the prevlence of known dibetes in The Netherlnds vries between 235,000 nd 285,000 known dibetic ptients or is % of the totl popultion. Systemtic screening with n OGTT yields prevlences which re twice s high. Depending on the intended ppliction, different estimtes cn be of use. Prevlence rtes bsed on selfreported dt my be used when estimting totl helth Downloded from by guest on 30 November 2018

6 Prevlence of dibetes mellitus cre use, while the prevlence bsed on cses reported by generl prctitioners my be of use for tht specific spect of the helth cre system. Prevlence rtes of dibetes bsed on screening re relevnt for preventive strtegies nd ltent helth cre needs. This study is prt of reserch project supported by grnts from the Ntionl Institute for Helth Sciences (N1HES). The uthors re grteful to P.J. vn der Ms, D. Kromhout, P.J. vn de Mheen, J. Brendregt, R.P. Stolk nd R. Gijsen for helpful comments nd E.H. vn de Lisdonk nd the stff of the deprtment of Generl Prctice in Nijmegen, R.P. Stolk nd D.J.H. Deeg for generously providing prevlence dt. 1 King H, Rewers M. Globl estimtes for prevlence of dibetes mellitus nd impired glucose tolernce in dults. Dibetes Cre 1993;16: Alberti KGMM. Problems relted to definitions nd epidemiology of type 2 (non-insulin-dependent) dibetes mellitus: studies throughout the world. Dibetologi 1993;3S: World Helth Orgniztion. World Helth Orgniztion Expert Committee on Dibetes Mellitus. Second report. Genev: WHO, World Helth Orgniztion. Dibetes mellitus: report of study group. Genev: WHO, My JF. Epidemiologic crdiology: ischemic hert disese study Vlgtwedde, 1970 [thesis]. Groningen: University of Groningen, Schellevis FG, vn de Lisdonk E, vn der Velden J, et l. Vlidity of dignoses of chronic disese in generl prctice: the ppliction of dignostic criteri. J Clin Epidemiol 1993;46: Reenders K, de Nobel E, vn Weel C. Dibetes mellitus in een groepsprktijk: 1. Dignostiek, controle en behndeling (Dibetes in generl prctice: 1. Dignosis, control nd tretment). Huisrts en Wetenschp 1988,31: Metsemkers JFM, Hoppener P, Knottnerus JA, Limonrd CBG. Helth problems nd dignoses in fmily prctice. Mstricht: Registrtion Network Fmily Prctices, University of Li m burg, Lmberts H. Morbidity in generl prctice: dignosis relted informtion from the Monitoring Project. Utrecht: Huisrtsenpers, vn de Mheen PJ. Prevlentie vn dibetes mellitus in verzorgingstehuizen (Prevlence of dibetes mellitus in nursing homes). Bilthoven: Rijksinstituut voor Volksgezondheid en Milieuhygiene, vn der Velden J, de Bkker DH, Clessens AAMC, Schellevis FG. Een ntionle studie nr ziekten en verrichtingen in de huisrtsprktijk. Bsisrpport: morbiditeit in de huisrtsenprktijk (A ntionl study for diseses nd opertions in the generl prctice: morbidity in the generl prctice). Utrecht: Netherlnds Institute of Primry Helth Cre, Steering Committee on Future Helth Scenrios. Chronische ziekten in het jr Volume 1: scenrio's vn dibetes mellitus (Chronic diseses in the yer 200S. Volume 1: scenrios on dibetes mellitus ). Dordrecht, Boston, London: Kluwer Acdemic Publishers, vn de Lisdonk EH, Bosch WJHM, Huygen FJA, Lgro-Jnsen ALM, editors. Ziekten in de huisrtsprkijk (Diseses in the generl prctice). Utrecht: Wetenschppelijke Uitgeverij Bunge, Cromme P, vn Eijk J, vn der Veen E, et l. 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7 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO Meyboom-de Jong B. Morbidity registrtion in generl prctice in The Netherlnds. Huisrts Wetenschp 1993;36(Suppl): Feskens EJM, Kromhout D. Glucose tolernce nd the risk of crdiovsculr diseses: the Zutphen Study. J Clin Epidemiol 1992;45(11): Wiener K. The dignosis of dibetes mellitus, including gesttionl dibetes. Ann Clin Biochem 1992;29: Ruwrd D. Dibetes mellitus: from epidemiology to helth policy [thesis]. Rotterdm: Ersmus University Rotterdm, Hrris Ml, Hmmn R. Dibetes in Americ. Wshington DC: NIH Wetterhll SF, Olson DR. DeStefno F, et l. Trends in dibetes nd dibetic complictions, Dibetes Cre 1992; 15: Received 3 Jnury 1997, ccepted 24 April 1997 Appendix In the first nlysis, the differences in prevlence estimtes between the studies were identified djusted for different ge structures, by using the following regression eqution: bgit (y)sex = bgit ( + pi x ge + P2 x study) where ge is continuous vrible nd the study is dummy vrible. In the second nlysis, the influence of methodologicl vrition on the prevlence of dibetes ws estimted by using the following regression eqution: bgit (y)sex = bgit ( + pi x ge + P2 x clender yer + p3 x Mr) where ge nd clnder yer re continuous vribles nd Mr is the methodology used: 0 is report by generl prctitioner nd 1 is self-report in survey. Downloded from by guest on 30 November 2018