WHO MONICA Project e-publications, No. 17
June 1999
Hanna Tolonen1 and Kari Kuulasmaa1 for the WHO MONICA Project2
1 MONICA Data Centre, National Public Health Institute, Helsinki, Finland
2 Annex: Sites and key personnel of the WHO MONICA
Project
Thanks are due to Alun Evans and Annette Dobson who commented on the text.
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. 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 Institute de Recherches Internationales Servier (IRIS), France, and Merck & Co. Inc., New Jersey, USA, to support data analysis and preparation of publications.
In the WHO MONICA Project (1), three independent cross-sectional population surveys were carried out in a large number of populations in the 1980s and early 1990s to measure the classical risk factors for the cardiovascular diseases. A specific question about the use of aspirin was introduced in the November 1990 version of the MONICA Manual (2). Since most of the MONICA Collaborating Centres (MCCs) had already started and many had even finished their middle population surveys by that time, this new question was considered an optional item in that survey. As a result, less than half of the MCCs had this question in their middle survey. In the final survey, the question was asked in most of the MCCs.
The MONICA Project has a standard format for data transfer to the common database. It is necessary to collect the information in such a format so that the data required for the data transfer can be extracted. The question on the use of aspirin in the MONICA Manual (2) is:
ASP "Are you taking (in the last two weeks) aspirin tablets to prevent or treat heart disease?"
1 = yes, taking tablets for this reason
2 = no, I am not taking aspirin tablets
3 = no, but I am taking tablets for reasons unconnected with heart condition
9 = insufficient data
The main purpose of this quality assessment report is:
The results of this document are reported by Reporting Unit Aggregates (RUAs) which are foreseen as potential candidates for the units of analysis of the MONICA data. The RUAs are identified by an abbreviation and a version letter. Only RUAs which have provided data to the MONICA Data Centre (MDC) for item ASP are considered in this report. These RUAs, their abbreviations and Reporting Units as well as the number of subjects in the surveys are listed in Table 1. Altogether 28 RUAs are considered for the middle survey and 31 for the final.
The original survey questionnaires in the local language and/or the English translations were available in the MDC for all RUAs (Table 2). In 1991 a questionnaire on the MONICA Population Survey Procedures (Form VI), including a question on whether the questionnaire was self-administered or completed during an interview, was sent to all MCCs. The questionnaire was further checked by the MCCs regarding the final survey in 1995.
The survey data on the use of aspirin was transferred to the MDC using the MONICA core data transfer format (Form 04, versions 6 and 7) (2). The item on the data transfer format remained unchanged throughout the middle and final surveys.
The age range studied in each RUA is given in Table 1. Age was defined as age in full years on the date of examination (see DEF1 in reference 3). No weighting was applied to the data.
As reported in Table 2, for the middle and final survey all RUAs have provided their original questionnaire and/or its English translation. In the final survey two RUAs (ICE-ICE and YUG-NOS) used the MONICA data transfer format (Form04) as their original questionnaire. YUG-NOS translated the questionnaire to Serbo-Croatian but ICE-ICE used the English version as their original questionnaire.
Findings
In the middle survey 3 out of 5 RUAs which have data for ASP used the standard MONICA format. UNK-GLA used the combination of two questions "Are you taking aspirin regularly?" and "If yes, is it for your heart" from which the exact MONICA data can be extracted. UNK-BEL asked the medicines used and aspirin was one of the alternatives, but the reason for taking it was not asked.
In the final survey 25 (81%) RUAs used the standard MONICA format. In 6 RUAs the formulation of the question is different from the standard MONICA format but the exact MONICA data can be extracted. In 3 RUAs (AUS-NEW, AUS-PER and USA-STA) the option "No, I am taking tablets for reasons unconnected with heart condition" was missing. In 2 RUAs (AUS-PER and CAN-HAL) the time period was past month and 2 RUAs (UNK-GLA and USA-STA) referred to the present time.
When the survey core data were received in the MDC, the data were checked routinely for the following constraint:
All violations of these constraints were reported to the MCC for their correction or elucidation. Data values outside the limits were acceptable, but the MCC had to check that the values were not unusual owing to data errors. The MCCs were asked to correct values only if they were incorrect. There are no unresolved constraint violations in the middle or final survey.
Table 3 presents the availability of data on ASP in each RUA, in the middle and final survey. In the middle survey data are available in 5 (18%) RUAs and in the final survey in all 31 RUAs. Among the RUAs which have collected the data on ASP the percentage availability is very high, ranging from 97% to 100% in the middle survey, and from 85% to 100% in the final survey.
The distribution of data on ASP is presented in Table 3. The proportion of answers 'No, but I am taking tablets for reasons unconnected with heart condition ' is zero in the middle survey in UNK-BEL (where the reason for taking aspirin was not asked) and in the final survey in FRA-LIL, RUS-NOI and USA-STA.
Table 4 gives the summary score for the quality of data for the item ASP in each RUA. The summary score and components were defined as:
a) Questionnaire compliance score
| Score = | 0 | if no questionnaire available at the MDC, no ASP question in the questionnaire, or the formulation as the question is significantly different from the standard format; |
| 1 | if an alternative formulation of the question was used, but it is considered to have only minor or no effect on prevalence estimates; | |
| 2 | for all other RUAs. |
b) Insufficient data score
| Score = | 0 | if proportion of "insufficient" data > 10%; |
| 1 | if proportion of "insufficient" data is 5%-10%; | |
| 2 | for all other RUAs. |
c) Summary score
| Score = | 0 | if the Questionnaire compliance score or Insufficient data score is 0; |
| 1 | if the average of Questionnaire compliance score and Insufficient data score is 1 after rounding; | |
| 2 | if the the average of Questionnaire compliance score and Insufficient data score if 2 after rounding. |
In the middle survey 5 RUAs have provided data for item ASP and all these RUAs have summary score 2. In the final survey 29 RUAs have summary score 2 and only 2 RUAs (DEN-GLO and SWE-GOT) have summary score 0. In both cases in the final survey where summary score is 0, the reason for the low summary score is a high proportion of missing data.
The data on use of aspirin were collected in the middle and final survey. Because the data for the initial survey are not available and in the middle survey there are only few RUAs which have provided the data, they cannot be used for trend analysis but can be used for cross-sectional analysis.
The use of a different time periods (past month or present time) should not cause bias because a person using aspirin now or during the past month has most likely also used it in the past two weeks.
The omission of the option "No, but I am taking tablets for reasons unconnected with heart condition" should not cause bias because in all cases where this option was omitted the local question specified the use to be limited to heart disease.
The data on use of aspirin were collected in 5 RUAs in the middle survey and in 31 RUAs in the final survey. In the middle survey in all 5 RUAs the data can be used for cross-sectional analysis. (Note, however, the exceptional question in UNK-BEL.) In the final survey data from 29 RUAs can be used for the cross-sectional analysis.
The following list includes only RUAs with specific findings or exceptional background information relevant for the use of data, and the RUAs for which additional clarification is expected.
AUS-NEW
AUS-PER
CAN-HAL
DEN-GLO
SPA-CAT
SWE-GOT
UNK-BEL
UNK-GLA
USA-STA