Curriculum in Cardiology Prediction of first coronary events with the Framingham score: A systematic review Klaus Eichler, MD, MPH,a Milo A. Puhan, MD, PhD,a Johann Steurer, MD, MME,a and Lucas M. Bachmann, MD, PhDa,b Zurich and Berne, Switzerland Background Uncertainty exists about the performance of the Framingham risk score when applied in different populations. Objective We assessed calibration of the Framingham risk score (ie, relationship between predicted and observed coronary event rates) in US and non-US populations free of cardiovascular disease. Methods We reviewed studies that evaluated the performance of the Framingham risk score to predict first coronary events in a validation cohort, as identified by Medline, EMBASE, BIOSIS, and Cochrane library searches (through August 2005). Two reviewers independently assessed 1496 studies for eligibility, extracted data, and performed quality assessment using predefined forms. Results We included 25 validation cohorts of different population groups (n = 128 000) in our main analysis. Calibration varied over a wide range from under- to overprediction of absolute risk by factors of 0.57 to 2.7. Risk prediction for 7 cohorts (n = 18 658) from the United States, Australia, and New Zealand was well calibrated (corresponding figures: 0.87-1.08; for the 5 biggest cohorts). The estimated population risks for first coronary events were strongly associated (goodness of fit: R 2 = 0.84) and in good agreement with observed risks (coefficient for predicted risk: h = 0.84; 95% CI 0.41-1.26). In 18 European cohorts (n = 109 499), the corresponding figures indicated close association (R 2 = 0.72) but substantial overprediction (h = 0.58, 95% CI 0.39-0.77). The risk score was well calibrated on the intercept for both population clusters. Conclusion The Framingham score is well calibrated to predict first coronary events in populations from the United States, Australia, and New Zealand. Overestimation of absolute risk in European cohorts requires recalibration procedures. (Am Heart J 2007;153:722231.e8.) Clinical guidelines for primary prevention of coronary heart disease (CHD) recommend a risk management based on the Framingham score.1,2 The Framingham score as applied in these guidelines is a tool to predict the absolute risk of coronary events in populations free of cardiovascular disease (CVD). It is available in different application formats (eg, point scoring systems, risk charts, or Web-based calculators) From the aHorten Centre for Patient Oriented Research, University hospital of Zurich, Postfach Nord, Zurich, Switzerland, and bDepartment of Social and Preventive Medicine, University of Berne, Berne, Switzerland. The study was supported by the Helmut Horten Foundation. The funding source had no influence on study design; in the collection, analysis, and interpretation of the data; in the writing of the manuscript; and in the decision to submit the manuscript for publication. Submitted October 26, 2006; accepted February 13, 2007. Reprint requests: Klaus Eichler, MD, MPH, Horten Centre, University Hospital of Zurich, Postfach Nord, CH-8091 Zurich, Switzerland. E-mail: [email protected] 0002-8703/$ - see front matter D 2007, Mosby, Inc. All rights reserved. doi:10.1016/j.ahj.2007.02.027 and requires only information from patient history and easily available tests.3 However, there is uncertainty about the performance of the Framingham score to predict absolute risk for first coronary events when applied in different populations. Validation studies showed inconsistent results across different populations4,5 leading to a debate about the appropriateness of this tool for risk prediction in Europe. Finally, it is important to ensure that CHD risk prediction is as accurate as possible for the group of patients to which it is applied.6 We aimed to systematically review all cohort studies that validated calibration (ie, relationship between predicted and observed event rates) of the Framingham risk score in US- and non-US populations free of CVD. Methods Data sources We systematically searched for studies of prediction rules for cardiovascular risk using electronic databases (Medline, EMBASE, BIOSIS, Cochrane library; from 1966 to August 2005; American Heart Journal Volume 153, Number 5 Eichler et al 723 Figure 1 Study flow of the systematic review. no language restriction). Validation studies of prediction rules are difficult to retrieve in electronic data bases because such studies are not indexed in a standardized manner. Thus, we used a sensitive search strategy not specific for the Framingham model but for cardiovascular prediction rules in general (see Appendix Table II for search strategy). We screened reference lists of included papers, contacted experts, and performed searches for related articles and citation searches of key references. We hand-searched relevant journals (Circulation, European Heart Journal, and Medical Decision Making) for supplements and conference proceedings. Where we did not find sufficient data for our analysis, we contacted authors. Of 21 contacted authors, 8 provided additional data. All references were stored in an EndNote 6.0 database (Thomson/ISI ResearchSoft, Berkeley, CA). Study selection We undertook the systematic review in accordance with current recommendations.7 We included studies with a prospective cohort design and cohorts derived from randomized trials. We defined a validation study as prospective if the data set of the validation population had been collected prospectively. Thus, a prospective validation study could be set up on a historical data set if it had been collected prospectively. American Heart Journal May 2007 724 Eichler et al Table I. Details of 24 validation cohorts of the Framingham risk score for main analysis Validation cohort4, location Author, y Brindle et al, 20035 Brindle, 200412 Cooper et al, 200513 DPCG, 20029 DPCG, 2002 DPCG, 2002 DPCG, 2002 DPCG, 2002 DPCG, 2002 DPCG, 2002 Empana et al, 200314 Empana et al, 2003 Ferrario et al, 200515 Greenland, 200416 Hense et al, 20034 Hense et al, 2003 Milne et al, 2003 17 Mora et al, 200518 Orford et al, 200219 Ramachandran et al, 200020 Simons, 200321 Stephens et al, 200422 British regional heart study cohort; United Kingdom Caerphilly and Speedwell cohort; United Kingdom NPHS-II; United Kingdom NHANES I, men; United States NHANES II, men; United States Scottish Collaborative Study, men; Scotland Renfrew and Paisley Study, men; United Kingdom Norwegian Counties Study, men; Norway Iceland Reykjavik Study, men; Iceland Yugoslavia Cardiovascular Disease Study, men; former Yugoslavia PRIME Study; Ireland PRIME Study; France CUORE cohorts, men; Italy Sample size (n) (men, %) Clinical outcomeyy (follow-up) 6643 (100%) NA (40-59), British, GP Total CHD (10 y) 3213 (100%) NA (45-63), British, general population Hard CHD (10 y) 2732 (100%) 3856 (100%) 56 (50-64), British, GP NA (35-74), US American, general population NA (35-74), US American, general population NA (35-72), Scottish, OCC Hard CHD (10 y) Death from CHD (8 y) NA (45-64), British, general population NA (35-49), Norwegian, general population NA (36-74), Icelandic, general population NA (35-64), Yugoslavian, general population Death from CHD (8 y) 3354 (100%) 5734 (100%) 6999 (100%) 24204 (100%) 8151 (100%) 6340 (100%) 2399 (100%) 7359 (100%) 5794 (100%) South Bay Heart Watch cohort, United States PROCAM cohort; Germany (Münster) MONICA cohort, men; Germany (Augsburg) Fletcher Challenge Heart and Health Study; New Zealand John Hopkins Sibling Study; United States Normative Aging Study; United States (Boston, MA) Wickham Study; England 1700 (44.2%) Dubbo Study; Australia 1800 (41.9%) University College London Hospitals cohort; United Kingdom Glostrup cohort; Denmark SHHEC; United Kingdom Mean age (range) (y), ethnicity, recruitment 1029 (90%) 5527 (100%) 2861 (100%) 6354 (73%) 872 (51%) 1393 (100%) 798 (63%) 4757 (50.1%) Thomsen et al, 200223 Tunstall-Pedoe and 13037 (49%) Woodward, 200524 WOSCOPS Group, 199825 WOSCOPS Group (placebo 1251 (100%) control group of RCT); Scotland NA (50-59), Irish, OCC, GP NA (50-59), French, OCC, GP NA (35-69), Italian, general population 67.5 (NA-NA), US American, general population 46.5 (35-64), German, OCC 49.5 (35-64), German, general population NA (35-74), ethnicity: see comment, OCC, general population 45.8 (NA-60), US American, family members 58.2 (30-74), Northern American, general population NA (30-75), English, general population NA (60-79), Australian, general population NA (35-74), ethnicity: see comment, University diabetes clinic Death from CHD (8 y) Death from CHD (8 y) Death from CHD (8 y) Death from CHD (8 y) Death from CHD (8 y) Total CHD (5 y) Total CHD (5 y) Total CHD (10 y) Hard CHD (7 y) Hard CHD (variable follow-up y) Hard CHD (variable follow-up y) CVD (71% of events were total CHD) (5 y) Total CHD (10 y) Total CHD (10 y) Total CHD (20 y) Hard CHD (10 y) Total CHD (10 y) 58.9 (49-70), Danish, general population Death from CHD (10 y) NA (30-74), Scottish, general population Total CHD (10 y) NA (45-64), Scottish, moderately hypercholesterinemic men Hard CHD (4 y) NA, Not available; OCC, occupational cohort; GP, cohort from general practitioner; ATP III, Adult Treatment Panel III; DPCG, Diverse Populations Collaborative Group; SHHEC, Scottish Heart Health Extended Cohort; RCT, randomized controlled trial. 4Design: prospective cohort study (if not stated otherwise). yDeath from CHD (includes fatal myocardial infarction; sudden or nonsudden coronary death); hard CHD (includes coronary revascularization; nonfatal myocardial infarction; death from CHD); total CHD (includes angina; coronary insufficiency; hard CHD); and CVD (includes total CHD, stroke [including transient ischemia], peripheral vascular disease, congestive heart failure). zBaseline risk: observed risk for an event in the validation cohort (for the reported follow-up period). §Predicted risk for an event when the Framingham model was applied to the validation cohort (for the given follow-up period). tValues b1.0 indicate underprediction; values N1.0 indicate overprediction. bThe number of quality items grouped to the categories byes,Q bno,Q and bnot clearQ. American Heart Journal Volume 153, Number 5 Eichler et al 725 Table I (continued) Baseline riskzz Predicted risk§§ Predictive capacity: P/Ot t Q-item (yes/no/ not clear)bb Comment 677 10.2% 16.0% P/O: 1.57 7/0/2 Data extracted for combined outcome (all coronary events) 276 8.6% 10.7% P/O: 1.24 7/0/2 Data extracted only for the first 10-y follow-up period 219 205 8.0% 5.3% 17.0% 5.0% P/O: 2.12 P/O: 0.94 6/2/1 6/0/3 Applied Framingham model: ATP III guidelines NHANES I 142 4.2% 4.6% P/O: 1.08 6/0/3 NHANES II 190 3.3% 2.1% P/O: 0.63 6/0/3 445 6.4% 3.8% P/O: 0.60 6/0/3 218 0.9% 1.4% P/O: 1.54 6/0/3 240 2.9% 3.3% P/O: 1.13 6/0/3 82 1.3% 1.6% P/O: 1.27 6/0/3 120 197 304 5.0% 2.7% 5.2% 6.7% 6.3% 14.2% P/O: 1.34 P/O: 2.35 P/O: 2.70 5/1/3 5/1/3 6/0/3 84 8.2% 11.2% P/O: 1.37 7/2/0 307 5.6% 9.8% P/O: 1.77 6/1/2 146 5.1% 10.2% P/O: 2.00 6/1/2 411 6.5% 5.6% P/O: 0.87 6/0/3 110 12.6% 8.4% P/O: 0.67 8/0/1 206 14.8% 15.9% P/O: 1.08 7/0/2 529 31.1% 23.6% P/O: 0.76 6/1/2 192 10.7% 11.6% P/O: 1.08 6/2/1 269 33.7% 19.2% P/O: 0.57 6/2/1 148 783 3.1% 6.0% 3.4% 8.9% P/O: 1.09 P/O: 1.49 5/1/3 6/2/1 87 7.0% 7.6% P/O: 1.09 6/2/1 Events (n) Participants included from different Italian cohorts Framingham model: ATP III guidelines; participants: volunteers at high risk for CHD Population: 85% European or other ethnicity, 10% Maori, 5% Pacific people; additional data from related article26 Population: siblings of hospitalized patients with premature CHD; 15% black Population: community dwelling men of the greater Boston area (98% white) Framingham model: ATP III guidelines; population: noninstitutionalized residents of the town Dubbo Population: 69% white, 23% Indian, 5% Afro-Caribbean, 3% Chinese 1251 of 3293 participants of the placebo control group of the WOSCOPS included in this analysis American Heart Journal May 2007 726 Eichler et al We applied the following end point definitions: CHD death (includes fatal myocardial infarction, sudden or nonsudden coronary death); hard CHD (includes coronary revascularization, nonfatal myocardial infarction, CHD death); total CHD (includes angina, coronary insufficiency, hard CHD); CVD (cardiovascular disease, includes total CHD, stroke [including transient ischemia], peripheral vascular disease, congestive heart failure). Studies had to evaluate the Framingham risk score in a validation population different from the derivation population8 and free of documented CVD at study entry. A comparison of predicted outcome events in the validation population (according to the Framingham risk score) with observed events in the validation population had to be provided. We did not focus on a specific version of the Framingham equation. We excluded studies investigating highly selected populations not representative for primary care (eg, patients with end stage renal disease), cohorts of trials with active intervention, cohorts with b70 events during follow-up,9 and studies with a considerable shorter follow-up period (ie, b80%) compared to the follow-up time of the risk prediction model. If data of a specific cohort were published in several papers or if follow-up data were presented, we included each cohort only once. Data extraction Two reviewers independently screened titles and abstracts for relevance and assessed potentially relevant studies for inclusion by full text. Agreement between reviewers was assessed using chance-adjusted n statistics. We resolved disagreements by consensus meetings. Data were extracted by one reviewer using a predefined form and checked independently by a second reviewer. We extracted data on general study information (eg, length of follow up, applied version of the Framingham risk score), study setting (eg, level of population recruitment), population details, predicted and observed events, and information about risk classes. We performed a quality assessment using selected criteria of methodological standards for observational studies.7,8,10 Our quality items covered aspects of internal and external validity (eg, assessment of outcome blinded for predictive variables; follow-up completeness; for details of quality assessment, see Appendix C). Statistical analysis First, we evaluated calibration of the Framingham score relying on data derived from risk classes. We generated a calibration plot with the observed risk ( y axis) and the predicted risk (x axis) for each cohort where information about risk classes was available. We assessed strength of association (as a prerequisite for adequate calibration) between predicted and observed risk estimates for different risk classes. We studied how closely the regression line of our model represented the data points (R 2, goodness of fit; % of variation explained with the model). A consistently strong association across several cohorts would allow for use of aggregated (population level) data for all remaining analyses. Second, we calculated the ratio of predicted risk to observed risk (P/O) for each validation cohort (with the number of predicted events according to the Framingham model in the numerator and the number of observed events in the validation cohort in the denominator). With a perfectly calibrated score, the predicted risk is the same as the observed risk (P/O ratio of 1.0). Third, we divided our data set into 2 prespecified subgroups to compare cohorts from Northern America, Australia, and New Zealand (where guidelines generally recommend the Framingham score) with cohorts from Europe (where additional risk scores are used). We constructed forest plots and calculated pooled estimates of the P/O ratio using a random effects model. Fourth, we assessed factors that may influence calibration for each population subgroup. With a metaregression analysis, we evaluated the influence of a priori chosen independent factors (eg, applied version of the Framingham model, start of followup, study size, or completeness of follow-up) on calibration. Finally, we generated a calibration plot for each population cluster. With a variance-weighted linear regression model, weighted for the reciprocal value of the square of the standard error of the baseline risk,11 we evaluated the relationship between babsolute observed risk in %Q (as dependent variable) and babsolute predicted risk in %Q (as independent variable). With this approach, we focused on two features of calibration, which are critical for application in practice: (1) (2) Strength of association (R 2: goodness of fit; as applied for risk classes) Agreement of predicted with observed absolute risk values: agreement is determined as the slope and the intercept of the regression line in the calibration plot; a slope of 1.0 (ie, h-coefficient for predicted risk: h = 1.0) and an intercept of zero (ie, a = 0.0) are identical with the 458 concordance line and indicate perfect agreement. A slope of N1.0 indicates underprediction, and a value of b1.0, overprediction. Analyses were performed using the STATA 8.2 software package (StataCorp 2004, Stata Statistical Software, College Station, TX). Results Description of validation studies Our searches retrieved 1496 potentially relevant studies (Figure 1). Seventeen validation studies of the Framingham risk score4,5,9,12-25 with 25 independent prospective validation cohorts met the inclusion criteria (for excluded studies, see Appendix Table IV). Agreement between reviewers was high (chance adjusted n statistics: 0.89). Seventeen cohorts provided data for hard CHD or total CHD. One cohort reported CVD outcomes, of which 71% were total CHD events,17 and in 8 cohorts, the outcome was CHD death (for study details, see Table I). Definitions of clinical events and of end point categories were often similar to Framingham criteria.27,28 For example, the World Health Organization MONICA diagnostic categories for myocardial infarction were American Heart Journal Volume 153, Number 5 Eichler et al 727 Figure 2 Calibration of 25 Framingham validation studies according to reported end points: death from CHD (A) and total or hard CHD (B). For each end point, group studies are sorted for increasing baseline risk (calculated as 10-year risk in %). For study acronyms and references, see Table I. Framingham model: Wilson*, Adult Treatment Panel III version2; DPCG, Framingham model of the Diverse Population Collaborative Group.9 derived from electrocardiogram, enzymes, symptoms, and autopsy findings.4 To determine end points during follow-up, mainly medical records as well as study registers (via International Classification of Diseases codes) were analyzed. Information about CHD death was also derived from death certificates (validated by chart review and autopsy findings, where available). A review panel for ascertainment of diagnoses was established in 8 cohorts. The 25 prospective validation cohorts included 128 000 persons. Population sizes varied from 798 to 24 204 participants (median 3856, interquartile range 1800-6354). Participants were recruited from general populations or occupational settings (n = 23 cohorts) and from clinics (n = 2 cohorts). Cohorts were set up in the United States (n = 5), in Europe (n = 18), and in Australia/New Zealand (n = 2). Age of participants in the validation cohorts ranged from 30 to 79 years at 728 Eichler et al American Heart Journal May 2007 Figure 3 Calibration of Framingham validation studies according to population groups: cohorts from the United States, Australia, and New Zealand (A) and from Europe (B). For each population group, studies are sorted for increasing baseline risk (calculated as 10-year risk). White rectangles represent cohorts reporting total or hard CHD; black triangles, cohorts reporting death from CHD. inclusion; the mean follow-up was 8.8 years (median 8 years, interquartile range 8-10) and started between 1961 and 1992. Observed event rates ranged from 4.8% to 33.7% for hard/total CHD and from 0.5% to 4% for CHD death end points. The Framingham equations published by Wilson27 and Anderson29 were used in 18 cohorts; in 7 cohorts, a proportional hazards Framingham function for CHD death was applied.9 cohort such as Framingham risk ranges or age ranges of participants). We found a consistently close linear association between predicted and observed estimates for risk classes within cohorts (range of the linear model fit for seven cohorts, R 2 = 0.903-0.998; for details, see Appendix A). Thus, we relied on aggregated (population level) data for our further analyses. Methodological quality Overall quality of studies for our main analysis (covering 25 cohorts) was moderate to good. Description of population recruitment and participant characteristics was given for all 25 cohorts. Information in detail for the clinical end points was provided in 24 of 25 cohorts; specific definitions of applied predictive variables were less often available (details given for 19 cohorts). For only 2 of 25 cohorts, information was available that outcome assessors were blinded for predictive variables.16,18 Information about completeness of inclusion (defined as inclusion of z75% of the screened population) and completeness of follow-up (defined as follow-up of z90% of the included population) was scarce (criteria fulfilled in 1 and in 7 of 25 cohorts, respectively). Calibration for different end points For cohorts reporting CHD death (Figure 2, A), calibration varied from underprediction (P/O 0.60 in a study from the United Kingdom9) to overprediction of absolute risk (P/O 1.54 in a cohort from Norway9). Variation was more pronounced for cohorts reporting total or hard CHD (from P/O 0.57 in a cohort from the United Kingdom22 to P/O 2.70 in a study from Italy,15 Figure 2, B). Pooled estimates of the P/O ratio were 0.99 (95% CI 0.85-1.16, I 2 = 98.4%) for cohorts reporting death from CHD and 1.30 (95% CI 1.10-1.52, I 2 = 99.2%) for total and hard CHD. Because the distribution pattern of P/O was similar for both outcome categories and fatal coronary events are known to be highly correlated with total coronary events,28 we relied on both outcome categories for our further analysis. Association of predicted and observed estimates for risk classes Six studies4,5,15,17,20,21 with 7 cohorts (2 cohorts from Australia/New Zealand and 5 from Europe) reported risk estimates for single risk classes (3-14 risk classes per Calibration for population clusters The Framingham score was well calibrated to predict absolute risk for the included seven cohorts from the United States, Australia, and New Zealand (n = 18 658) (Figure 3, A). The 5 biggest studies American Heart Journal Volume 153, Number 5 Eichler et al 729 Figure 4 Association between predicted and observed coronary heart disease event rates using a weighted linear regression model: cohorts from the United States, Australia, New Zealand (A) and from Europe (B). Each circle represents a single cohort. The circle area represents the weight given to each cohort in the linear regression model. The solid fitting lines show the relationship between predicted and observed risk. Data points above the dashed 458 concordance line represent underprediction; data points below this line represent overprediction. showed a P/O ratio between 0.87 and 1.08, and the pooled estimate for 7 studies was 0.99 (95% CI 0.90-1.10, I 2 = 96.6%). For the 18 cohorts of various European populations (n = 109 499) (Figure 3, B), calibration varied over a wider range (P/O ratio: minimum 0.57, maximum 2.70) with 14 of 18 studies showing overprediction of risk. The pooled P/O ratio for 18 European studies was 1.28 (95% CI 1.08-1.51, I 2 = 99.2%). In our metaregression analysis, we did not find a significant association of our predefined factors (eg, applied version of the Framingham model) with the P/O ratio in both population clusters. The linear regression model showed a strong association between predicted and observed population risks (R 2 = 0.84) for the 7 cohorts from the United States, Australia, and New Zealand (Figure 4, A). In addition, agreement of predicted and observed absolute risk was high (coefficients for predicted risk: h = 0.84 [95% CI 0.41-1.26]; a = .01 [95% CI 0.02 to 0.04]) with the regression line near to the 458 concordance line. For the 18 European cohorts, predicted and observed risk estimates were closely associated too (R 2 = 0.72) (Figure 4, B). Although the regression line was well calibrated on the intercept (a = .003 [95% CI 0.01 to 0.01], the overall agreement of predicted and observed absolute risk was poor because of substantial overprediction (h = .58, 95% CI 0.39-0.77). A sensitivity analysis showed that the results remained basically unchanged after exclusion of 2 studies with high event rates of N30%20,22 or of one study that also reported CVD events.17 Discussion The Framingham risk score is well calibrated to predict absolute risk for first coronary events in populations from the United States, Australia, and New Zealand. Mean predicted and observed population risk estimates are closely associated and show a high agreement. In European populations, overall agreement of predicted and observed absolute risk is poor due to substantial overestimation. Strengths and limitations We applied a thorough search strategy with a stepwise retrieval of studies using electronic databases and additional sources. We cannot exclude having missed validation studies, but we believe that we found a near complete sample of relevant papers. For study selection, we insisted on accepted methodological standards for validation studies and were interested in transferability of results to primary care. The analysis on the population level was based on the assumption that the consistency in the relationship American Heart Journal May 2007 730 Eichler et al between predicted and observed estimates for risk classes in 7 cohorts would also apply for the remaining studies. We believe that this approach is reasonable. The strong linear relationship was detectable in cohorts of both population subgroups. While the ideal way for this research question is by using individual patient data, we had to rely on aggregated study data. Thus, the observed relationships are relevant to the populations that comprise the 25 cohorts. Inferring these populationbased results to risk prediction in individuals may lead to bias known as ecological fallacy.30 In addition, the relatively low number of studies in the United States/ Australia/New Zealand group reduced precision of the regression coefficients, and the 95% CIs for the slope of the regression lines of both population clusters overlap. We interpreted pooled estimates cautiously because statistical heterogeneity between studies was considerable, and metaregression did not reveal significant associations of study descriptors with study results. However, we judge the analyzed cohorts as fairly similar from a clinical and methodological point of view (cohorts mostly population-based, participants free of CVD, and of similar age ranges; comparable length of follow-up; definitions of outcome categories similar to Framingham criteria). We did not evaluate discriminative ability of the Framingham risk score (ie, how well high- and low-risk groups are discriminated on the basis of the score) and focused on calibration. Although discrimination is an important feature of prediction rules, the results are difficult to interpret for clinicians,31 and calibration, that is, agreement of predicted with observed absolute risk, shows a higher variability between populations.32 Existing systematic reviews and implications for practice Because validation studies of the Framingham score show inconsistent results, we believe that a systematic review of this prognostic prediction rule is an appropriate approach to weight the overall evidence. Much work has been done in a systematic review by D’Agostino et al32 who addressed calibration in US cohorts of multiple ethnic groups. We were not able to extract sufficient information for predicted and observed events to include data of this study in our systematic review. A recent review by Brindle et al33 has also assessed the accuracy of risk assessment with the Framingham score for primary prevention of cardiovascular disease. This review differs from ours: we excluded 7 studies that were included by Brindle et al but did not meet our inclusion criteria (cohorts with up to 20% of persons with established CVD, active intervention groups of clinical trials, or cohorts with b70 events). Conversely, we included 8 studies that reported CHD death end points, retrieved 4 additional more recent studies with a search up to August 2005, and performed a formal assessment of heterogeneity and study quality.34 In addition, our approach to assess different population subgroups separately had substantial influence on the overall interpretation of results. Guidelines from the United States,2 Australia,35 and New Zealand36 have incorporated the Framingham risk score in their recommendations for risk assessment in primary prevention of CHD. This systematic review adds further empiric foundation for this decision. The Framingham risk score is an adequate instrument to estimate absolute coronary risk in populations free of CVD from the United States, Australia, and New Zealand. The Framingham score, in its present form, leads to substantial overprediction of coronary risk in European populations, which may be due to different risk factor distributions and event rates.32 Accordingly, one might consider a recalibration procedure of the Framingham score with European data to account for this overestimation.5,37 Similar activities have been undertaken for populations from Asia,38 and additional epidemiological research may be needed in other regions to evaluate transferability of the Framingham score worldwide. To intend a more precise risk prediction in European populations, the third Joint European Guidelines39 recommend the use of the EU-SCORE, a risk score based on data from European cohort studies. Whether this instrument, however, shows a stronger association and higher agreement between predicted and observed risk estimates compared to a recalibrated Framingham score merits further research in a direct comparison in European populations. Conclusion The Framingham risk score is an adequate instrument to estimate risk of first coronary events in populations from the United States, Australia, and New Zealand. Estimation of absolute risk for first coronary events in European cohorts is limited by overprediction and requires adjustment. We thank Dr Alfons Kessels (MD, MSc; statistician, Department of Clinical Epidemiology and Medical Technology Assessment, University Hospital Maastricht, The Netherlands) for methodological and statistical advice. We would like to especially acknowledge the helpful assistance of Dr. Ewout W. Steyerberg, (PhD, Center for Medical Decision Making, Department of Public Health, Erasmus MC, University Medical Center, Rotterdam, The Netherlands) for methodological support and critical review during manuscript writing. References 1. Wood D. Joint British recommendations on prevention of coronary heart disease in clinical practice. Heart 1998;80:S1-S29. American Heart Journal Volume 153, Number 5 2. 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A cross-validation of risk scores for coronary heart disease mortality based on data from the Glostrup Population Studies and Framingham Heart Study. Int J Epidemiol 2002;31:817 - 22. 24. Tunstall-Pedoe H, Woodward M. By neglecting deprivation cardiovascular risk scoring will exacerbate social gradients in disease. Heart 2006;92:307 - 10. 25. West of Scotland Coronary Prevention Study Group. Influence of pravastatin and plasma lipids on clinical events in the West of Scotland Coronary Prevention Study (WOSCOPS). Circulation 1998;97:1440 - 5. 26. Milne R, Gamble G, Whitlock G, et al. Discriminative ability of a risk-prediction tool derived from the Framingham Heart Study compared with single risk factors. N Z J Med 2003;116:U663. 27. Wilson PW, D’Agostino RB, Levy D, et al. Prediction of coronary heart disease using risk factor categories. Circulation 1998;97:1837 - 47. 28. Anderson KM, Odell PM, Wilson PW, et al. Cardiovascular disease risk profiles. Am J Heart 1990;121:293 - 8. 29. 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Heart 2006 Accessed at http://heart.bmjjournals.com/cgi/eletters/ hrt.2006.087932v3 [on 5 July 2006]. 35. The Cardiac Society of Australia and New Zealand. Lipid management guidelines–2001. National Heart Foundation of Australia, The Cardiac Society of Australia and New Zealand. Med J Aust 2001;175(Suppl):S57. 36. Jackson R. Updated New Zealand cardiovascular disease riskbenefit prediction guide. BMJ 2000;320:709 - 10. 37. Marrugat J, R DA J, Sullivan L, et al. An adaptation of the Framingham coronary heart disease risk function to European Mediterranean areas. J Epidemiol Community Health 2003;57:634 - 8. 38. Liu J, Hong Y, Agostino DRBS, et al. Predictive value for the Chinese population of the Framingham CHD risk assessment tool compared with the Chinese Multi-Provincial Cohort Study. JAMA 2004;291:2591 - 9. 39. De Backer G, Ambrosioni E, Borch-Johnsen K, et al. European guidelines on cardiovascular disease prevention in clinical practice: third joint task force of European and other societies on cardiovascular disease prevention in clinical practice (constituted by representatives of eight societies and by invited experts). Eur J Cardiovasc Prev Rehabil 2003;10:S1-S10. American Heart Journal May 2007 Eichler et al 731.e1 Appendix A Figure 5 Association between predicted and observed coronary heart disease event rates using estimates from risk classes: cohorts with data for risk classes from Australia and New Zealand (Figure 5, A) and European cohorts (Figure 5, B). Each data point represents a single risk class. For each risk class, bpredicted riskQ is plotted against bobserved risk.Q R 2, linear model fit. References of validation cohorts: Australia, Dubbo cohort, Simons et al21; New Zealand, Fletcher CHH Study, Milne et al17; United Kingdom, Caerphilly and Speedwell, Brindle et al5; Germany, MONICA, Hense et al4; Germany, PROCAM, Hense et al4; United Kingdom, Wickham Study, Ramachandran et al20; Italy, CUORE, Ferrario et al.15 American Heart Journal Volume 153, Number 5 731.e2 Eichler et al Appendix B. Detailed search strategy Query Number Database Search terms Search terms in MEDLINE (MEZZ): 1 MEZZ 2 MEZZ 3 MEZZ 4 MEZZ 5 MEZZ 6 MEZZ 7 MEZZ 8 MEZZ 9 MEZZ 10 MEZZ 11 MEZZ 12 MEZZ 13 MEZZ 14 MEZZ 15 MEZZ 16 MEZZ 17 MEZZ 18 MEZZ 19 MEZZ 20 MEZZ 21 MEZZ 22 MEZZ 23 MEZZ 24 MEZZ 25 MEZZ 26 MEZZ 27 MEZZ 28 MEZZ 29 MEZZ 30 MEZZ 31 MEZZ 32 MEZZ CARDIOVASCULAR-DISEASES# RISK# RISK.TI. PREDICT$ DECISION$ DECISION-SUPPORT-TECHNIQUES# 1 AND 2 AND 3 FRAMINGHAM NCEP NATIONAL WITH CHOLESTEROL WITH EDUCATION SYSTEMATIC WITH RISK WITH EVALUATION EUROP$5 WITH SCORE PROCAM MONICA SHEFFIELD BRHS BRITISH WITH REGIONAL WITH HEART DUNDEE BHF (BRITISH NATIONAL) WITH HEART WITH FOUNDATION GCRS GLOBAL WITH RISK PRIME WITH STUDY FINRISK FINNMARK SCOTTISH WITH HEART GLOSTRUP BIRNH RIFLE PARIS WITH PROSPECTIVE CATALONIA WITH HEART FACTORY WITH HEART 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 4 AND 31 Search terms in BIOSIS (BIZZ): 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 CARDIOVASCULAR-RISK 145$3.CC. RISK.TI. RISK.DE. 35 36 34 AND 37 33 38 39 AND (PREDICT$5 DECISI$10) FRAMINGHAM NCEP NATIONAL WITH CHOLESTEROL WITH EDUCATION SYSTEMATIC WITH RISK WITH EVALUATION EUROP$5 WITH SCORE PROCAM MONICA SHEFFIELD BRHS BRITISH WITH REGIONAL WITH HEART DUNDEE BHF BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ American Heart Journal May 2007 Eichler et al 731.e3 Appendix B (continued) Query Number Database Search terms in BIOSIS (BIZZ): 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ BIZZ Search terms in EMBASE (EMZZ): 69 EMZZ 70 EMZZ 71 EMZZ 72 EMZZ 73 EMZZ 74 EMZZ 75 EMZZ 76 EMZZ 77 EMZZ 78 EMZZ 79 EMZZ 80 EMZZ 81 EMZZ 82 EMZZ 83 EMZZ 84 EMZZ 85 EMZZ 86 EMZZ 87 EMZZ 88 EMZZ 89 EMZZ 90 EMZZ 91 EMZZ 92 EMZZ 93 EMZZ 94 EMZZ 95 EMZZ 96 EMZZ 97 EMZZ 98 EMZZ 99 EMZZ 100 EMZZ 101 EMZZ 102 EMZZ Search terms (BRITISH NATIONAL) WITH HEART WITH FOUNDATION GCRS GLOBAL WITH RISK PRIME WITH STUDY FINRISK FINNMARK SCOTTISH WITH HEART GLOSTRUP BIRNH RIFLE PARIS WITH PROSPECTIVE CATALONIA WITH HEART FACTORY WITH HEART 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 40 AND 67 CARDIOVASCULAR-DISEASE# RISK.TI. CARDIOVASCULAR-RISK 69 AND 70 71 72 73 AND (PREDICT$ DECISI$10) FRAMINGHAM NCEP NATIONAL WITH CHOLESTEROL WITH EDUCATION SYSTEMATIC WITH RISK WITH EVALUATION EUROP$5 WITH SCORE PROCAM MONICA SHEFFIELD BRHS BRITISH WITH REGIONAL WITH HEART DUNDEE BHF (BRITISH NATIONAL) WITH HEART WITH FOUNDATION GCRS GLOBAL WITH RISK PRIME WITH STUDY FINRISK FINNMARK SCOTTISH WITH HEART GLOSTRUP BIRNH RIFLE PARIS WITH PROSPECTIVE CATALONIA WITH HEART FACTORY WITH HEART 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 74 AND 101 American Heart Journal May 2007 731.e4 Eichler et al Appendix C. Details of quality assessment of 25 validation cohorts of the Framingham risk score: Author, y Brindle et al, 20035 Brindle, 200412 Cooper et al, 200513 DPCG, 20029 DPCG, 20029 DPCG, 2002 DPCG, 2002 DPCG, 2002 DPCG, 2002 DPCG, 2002 Empana et al, 200314 Empana et al, 2003 Ferrario et al, 200515 Greenland et al, 200416 Hense et al, 20034 Hense et al, 2003 Milne et al, 200317 Mora et al, 200518 Orford et al, 200219 Ramachandran et al, 200020 Simons et al, 200321 Stephens et al, 200422 Q-item 1 Q-item 2 Q-item 3 Q-item 4 Outcome assessment: blinded* Follow-up: lengthyy Follow-up: completenesszz Population: characteristics§§ British regional heart study cohort Caerphilly and Speedwell cohort NPHS-II NHANES I, men NHANES II, men Scottish Collaborative Study, men Renfrew and Paisley Study, men Norwegian Counties Study, men Iceland Reykjavik Study, men Yugoslavia Cardiovascular Disease Study, men PRIME Study, Ireland PRIME Study, France CUORE cohorts, men South Bay Heart Watch cohort MONICA cohort, men PROCAM cohort Fletcher Challenge Heart and Health Study John Hopkins Sibling Study Normative Aging Study Wickham Study ? ? ? ? ? ? ? ? ? + + + + + + + + + + + ? ? ? ? ? ? ? ? + + + + + + + + + + ? ? ? + ? ? ? + + + + + + + ? ? ? + + ? + + + + + + + + ? ? + + + + + + + + + Dubbo Study University College London Hospitals cohort Glostrup cohort SHHEC ? + + + + + ? + + ? ? + + ? + + Validation cohort Thomsen et al, 200223 Tunstall-Pedoe and Woodward, 200524 WOSCOPS Group, 199825 WOSCOPS (placebo control group of RCT) The symbols refer to the result of the quality assessment: b+,Q criterion fulfilled; b,Q criterion not fulfilled; b?,Q no information available; DPCG, Diverse Populations Collaborative Group; SHHEC, Scottish Heart Health Extended Cohort. *Assessment of outcome blinded for predictive variables: fulfilled if stated in the text or all cause mortality is the outcome. yFollow-up length in the validation cohort comparable to the follow-up time of the prediction rule: fulfilled if longer than 80% (or accounted for shorter follow-up in analysis). zCompleteness of follow up: fulfilled if completeness z90%. §Population characteristics described in sufficient detail: fulfilled if at least data for sex, age, and morbidities are provided. tRecruitment of population described in sufficient detail: fulfilled if qualitative description is provided. bCompleteness of inclusion of eligible patients (participation rate): fulfilled if completeness z75%. #Q-items indicates the number of quality items grouped to the categories yes (+), no (), and not clear (?). American Heart Journal May 2007 Eichler et al 731.e5 Q-item 5 Q-item 6 Q-item 7 Q-item 8 Q-item 9 Q-items Population: recruitmentt Inclusion: completenessb Predictive variables: definition provided Outcome: definition provided Math. techniques: description provided (Yes/ no/ not clear)# ? + ? ? ? ? ? ? ? ? + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 7/0/2 7/0/2 6/2/1 6/0/3 6/0/3 6/0/3 6/0/3 6/0/3 6/0/3 6/0/3 ? ? ? ? ? ? + + + + + + + + + + + + + + + + + + + + + + + + 5/1/3 5/1/3 6/0/3 7/2/0 6/1/2 6/1/2 6/0/3 ? ? ? + + + + + + + + + + + 8/0/1 7/0/2 6/1/2 ? + + + + + + + 6/2/1 6/2/1 ? + + + + + + + 5/1/3 6/2/1 + + + + 6/2/1 American Heart Journal Volume 153, Number 5 731.e6 Eichler et al Appendix D. Details of excluded studies (sorted for author) Author, y Validation cohort*, location Sample size, n Recruitment Clinical outcomey follow-up) Assmann et al, 200240 PROCAM cohort; Germany 5389 OCC Hard CHD (10 y) Bastuji et al, 200241 INSIGHT cohort (from RCT); Europe 4147 Hospital hypertension centers in Italy and GP in the remaining countries Total CHD (4 y) Boutouyrie et al, 200242 Hopital Broussais cohort; France 1045 Total CHD (NA) Brand et al, 197643 Western Collaborative Group Study cohort; United States 3154 Outpatient hypertension clinic of a Paris hospital OCC Total CHD (12 y) D’Agostino et al, 200132 6 Ethnically diverse US cohort studies 23424 NA Hard CHD (5 y) Ducimetiere et al, 198044 Paris Prospective Study cohort; France 7434 OCC Hard CHD (9 y) Dunder, 200445 ULSAM cohort; Sweden LRC Study cohort; United States 1108 50-year-old men from Uppsala Random sample of North American clinics Hard CHD (10 y) 428 GP Total CHD (10 y) Kornitzer and Koyunco, 200048 Poole Diabetes study cohort; United Kingdom Belgian Physical Fitness Study cohort; Belgium 2186 OCC Total CHD (10 y) Kornitzer and Koyunco, 2000 BIRNH cohort; Belgium 6068 Randomly chosen subjects from 4 communes Total CHD (10 y) Liu et al, 200438 Chinese CMCS cohort; China 30121 Centers of MONICA-sino project Hard CHD (10 y) Grover et al, 199546 Guzder et al, 200547 3678 Total CHD (12 y) Reason for exclusion Not sufficient data to assess the association between predicted and observed risk; PROCAM cohort covered with data from Hense et al4 Cohort of trial with active intervention in both groups (RCT of hypertension treatment: nifedipine vs co-amilorid) b70 Events during follow-up Different follow up in the validation cohort compared to the applied risk model Not sufficient data to assess the association between predicted and observed risk Not sufficient data to assess the association between predicted and observed risk b70 Events during follow-up Not sufficient data to assess the association between predicted and observed risk b70 Events during follow-up. Not sufficient data to assess the association between predicted and observed risk; b70 events during follow-up. Not sufficient data to assess the association between predicted and observed risk Not sufficient data to assess the association between predicted and observed risk American Heart Journal May 2007 Eichler et al 731.e7 Appendix D (continued) Author, y Validation cohort*, location Sample size, n Menotti et al, 200049 IRA cohort (Italian Rural Area); Italy 1656 Jimeno Mollet et al, 200550 Protopsaltis et al, 200451 Raval Sud Study cohort; Spain Piraeus Diabetes Centre Database; Greece Schulz et al, 200352 Recruitment Clinical outcomey follow-up) Total CHD (10 y) 112 Sample of 2 rural communities in northern and central Italy NA Total CHD (10 y) 339 NA Total CHD (10 y) Bad Bevensen cohort; Germany 42 Hard CHD (10 y) Shang et al, 200453 Stern et al, 200454 Japanese Collaborative Cohort Study; Japan SAHS cohort; United States 359 Patients referred to hospital for cardiologic evaluation OCC Suka et al, 200255 Japanese cohort; Japan von Eckardstein et al, 200456 Wang and Hoy, 200557 2570 Total CHD (10 y) Total CHD (10 y) 5611 Randomly selected from 3 types of neighborhoods in San Antonio, TX OCC Total CHD (10 y) PROCAM cohort; Germany 4818 OCC Hard CHD (10 y) Australian Aboriginal cohort; Australia 687 Community wide screening program Total CHD (10 y) Reason for exclusion Not sufficient data to assess the association between predicted and observed risk b70 Events during follow-up Not sufficient data to assess the association between predicted and observed risk b70 Events during follow-up b70 Events during follow-up Not sufficient data to assess the association between predicted and observed risk Different follow up in the validation cohort compared to the applied risk model Not sufficient data to assess the association between predicted and observed risk. PROCAM cohort covered with data from Hense et al 4 b70 Events during follow-up RCT, randomized controlled trial. *Design: prospective cohort study (if not stated otherwise). yDeath from CHD (includes fatal myocardial infarction; sudden or nonsudden coronary death); hard CHD (includes coronary revascularization; nonfatal myocardial infarction; death from CHD); total CHD (includes angina; coronary insufficiency; hard CHD); and CVD (includes total CHD, stroke [including transient ischemia], peripheral vascular disease, congestive heart failure). 731.e8 Eichler et al References of Appendix 40. Assmann G, Cullen P, Schulte H. Simple scoring scheme for calculating the risk of acute coronary events based on the 10-year follow-up of the Prospective Cardiovascular Munster (PROCAM) study. Circulation 2002;105:310 - 5. 41. Bastuji S, Garin A, Deverly D, et al. The Framingham prediction rule is not valid in a European population of treated hypertensive patients. J Hypertens 2002;20:1973 - 80. 42. 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