February 2000
Hugh Tunstall-Pedoe1, Markku Mähönen2, Zygimantas Cepaitis2, Kari Kuulasmaa2, Diego Vanuzzo3, Michael Hobbs4 and Ulrich Keil5 for the WHO MONICA Project6
1Cardiovascular Epidemiology Unit, (MONICA Quality Control Centre for Event
Registration), University of Dundee, Ninewells Hospital and Medical School, Dundee,
Scotland, U.K.
2 Department of Epidemiology and Health Promotion (MONICA Data Centre),
National Public Health Institute, KTL, Helsinki, Finland
3 Centre for Cardiovascular Diseases, A.S.S.4 "Medio Friuli", Udine,
Italy
4 Department of Public Health, University of Western Australia, Perth,
Australia
5Department of Epidemiology and Social Medicine, University of Münster,
Münster, Germany
6 Annex: Sites and key personnel of the WHO MONICA
Project
Correspondence to: h.tunstallpedoe@dundee.ac.uk
A report on the quality assessment of acute coronary care data in the WHO MONICA Project has been published in the World Wide Web [1]. Here we describe the derivation of an acute coronary care quality score for the purposes of an analysis of the relationship between acute coronary care and coronary endpoints, which has been published in the Lancet [2].
The ACC quality score is defined for the two periods (Period 1 and Period 2) of data collection specified in table 2 of reference [2]. It is combined from three components:
Def discrepancy is an index of the difference in the changes in treatment percentages from Period 1 to Period 2, when missing and incomplete records are included (Definition A) or excluded (Definition B) from the denominator. The treatment percentage is expressed as the Equivalent Treatment Score (ETS), which is the arithmetic mean of the eight percentages of patients with non-fatal definite myocardial infarction treated with:
The percentages and their differences between periods 1 and 2 and between Definitions A and B are shown in Table 1. If a population had acute coronary care records on every coronary event, and the use of the drug or treatment was always coded yes or no, there is no discrepancy. If records were missing, or some were coded "not known" for the item, then there would be a discrepancy.
Def discrepancy (Table 2) is derived from the difference of the change from Period 1 to Period 2 in ETS between the two definitions of denominators (Def A and Def B) (see Def A - Def B in Table 1) as:
| Def discrepancy score = | 20 points | if Def A - Def B = 0.0 - 0.2 |
| 15 points | if Def A - Def B = 0.3 - 0.5 | |
| 10 points | if Def A - Def B = 0.6 - 1.5 | |
| 5 points | if Def A - Def B = 1.6 - 2.5 | |
| 0 points | if Def A - Def B > 2.5 |
These two scores are derived from the overlap between the acute coronary care and the coronary event (CE) periods of recording specified in table 2 of reference [2]. Where the three or four year period of recording of coronary events is completely matched by data on acute coronary care there is 100% overlap and no asymmetry. Particularly in the first period of recording of acute coronary care, the period of recording of coronary events was more extensive, so that these two codes record the degree of overlap and the lack of symmetry in the periods. The rationale for this is that a comparatively long period of event recording was necessary to estimate precisely the case fatality, coronary event rate and coronary heart disease mortality rate, and that best scores were given to those populations in which acute coronary care recording was coextensive, or at least centred on this.
The Coextensive score and Symmetry score were derived separately from each of the two periods of recording.
Coextensive score was derived from percentage overlap = (Duration of ACC period / Duration of coronary event period)*100%.
| Coextensive score = | 5 points | if percentage overlap = 100% |
| 4 points | if percentage overlap = 66-99% | |
| 3 points | if percentage overlap = 33-65% | |
| 2 points | if percentage overlap < 33% |
Symmetry score is derived by subtracting the smaller from the larger length of time in months by which the coronary-event period extends beyond each end of the ACC period (which may be zero at one end). Calculation of months involved may involve averaging where alternate months were recorded.
| Symmetry score = | 5 points | if the CE period is symmetrical on the ACC period |
| 4 points | if the asymmetry is less than 9 months | |
| 3 points | if the asymmetry is 9-17 months | |
| 2 points | if the asymmetry is at least 18 months |
The Coextensive and Symmetry scores for each MONICA population and each period are listed in Table 2. The score is derived from both periods and is the same for both sexes so that there is only one value for each population.
The ACC quality score is calculated by dividing the sum of all the constituent scores (Def discrepancy, Coextensive and Symmetry scores for period one, Coextensive and Symmetry scores for period two) by 20. The maximum sum is 40 (=20+5+5+5+5) so best ACC quality score is 2.0. The ACC quality scores are listed in Table 2.
The MONICA Centres are funded predominantly by regional and national governments, research councils, and research charities. Coordination is the responsibility of the World Health Organization (WHO), assisted by local fund raising for congresses and workshops. WHO also supports the MONICA Data Centre (MDC) in Helsinki. Not covered by this general description is the ongoing generous support of the MDC by the National Public Health Institute of Finland, and a contribution to WHO from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA for support of the MDC and the Quality Control Centre for Event Registration in Dundee. The completion of the MONICA Project is generously assisted through a Concerted Action Grant from the European Community. Likewise appreciated are grants from ASTRA Hässle AB, Sweden, Hoechst AG, Germany, Hoffmann-La Roche AG, Switzerland, the Institut de Recherches Internationales Servier (IRIS), France, and Merck & Co. Inc., New Jersey, USA, to support data analysis and preparation of publications.