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Pilot-onderzoek voor het PIENTER-project: vragenlijstevaluatie (evaluatierapportage deel III)Melker HE de; Suijkerbuijk AWM, Heisterkamp SH; Conyn-van Spaendonck MAE; CIE (Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1995-04-30)INTRODUCTION In 1994 a pilot-study of the so-called PIENTER-project was carried out. The aim of this project is to establish a serum bank of a representative sample of the Dutch population. The serum bank will be used to estimate age-specific immunity of the general population against childhood diseases of the Netherlands Immunisation Programme, the incidence of infectious diseases with a frequent subclinical course and the prevalence of serum-derterminants of other illnesses. The questionnaire used in the pilot-study was evaluated in order to develop a questionnaire for the nation-wide data collection. AIM Evaluation of the questionnaire used for data collection in a pilot of a cross-sectional population-based study in the province of Utrecht. METHODS A sample of four municipalities weighted by the number of inhabitants was taken out of the municipalities in the Province of Utrecht. 510 persons in the age strata 0, 1-4, 5-9 to 75-79 years were randomly selected from the populations registers of these four municipalities. The participants have been asked to give some blood and to fill in a questionnaire. They have been requested to bring their vaccination certificates of the Dutch immunisation programme, of vaccination on the occasion travelling to the tropics and of military service. These vaccination data were registered on a study form. The opinion of the participants on the length and clarity of the questionnaire and the frequency of missing values for all questions were described. The population proportions weighted by age for self-reported vaccination history and the relation with religion were given. Self-reported vaccination history for diphteria, pertussis, tetanus, poliomyelitis and mumps, measles and rubella was compared with information on the vaccination history derived from the vaccination certificate of the Dutch immunisation programme. The proportions weighted by age for self-perception of health status, nationality and level of education were compared with the figures of the Netherlands Central Bureau of Statistics for the Dutch general population. The expected number of persons in subgroups for level of education, religion, nationality, ethnicity and participation on the Dutch immunisation programme in the nation-wide study were calculated on the basis of results of the pilot. In order to calculate the expected precision of the estimates of the seroprevalence in these subgroups to be reached in the nation-wide study, the serological results for hepatitis A in the pilot were used. RESULTS AND CONCLUSIONS The results confirm a difference in vaccination history and attitude of persons who belong to specific religious groups who reject vaccination. These persons reported more frequent that they were not (completely) vaccinated and adhere more often the opinion that vaccination was not necessary. They also reported more frequently principal refusal as the reason for incomplete vaccination. However, most persons who belong to a religion from which it is known that vaccination is refused, reported that vaccination was completed. As religion and vaccination history are correlated, it is important for the analysis of seroprevalence data to collect data on religion. The self-reported vaccination history for diphtheria, pertussis, tetanus, poliomyelitis, mumps, measles and rubella did not agree with the vaccination certificates of the Dutch immunisation programme. Participants frequently reported that the questions on vaccination history were not clear to them. Therefore in the nation-wide study questions on vaccination history will be limited. Information on vaccination history registered in the vaccination certificates of the Dutch immunisation programme will be collected. In comparison with the figures from the Central Bureau of Statistics persons without the Dutch nationality were underrepresented in the pilot of the Pienter-project. The participants of the Pienter-project might have been not representative for the level of education. The self-perception of health status were comparable with the Central Bureau of Statistics. The precision of seroprevalence to be expected in the nation-wide data collection seems reliable for subgroups of sex, level of education and persons who report to have participated in the Dutch immunisation programme. In contrast no subgroup analysis (unless special actions are taken to increase the response) will be possible for persons with a non-Dutch nationality or ethnicity. For reliable seroprevalence estimates for persons (younger than 40 year) who have not participated in the Dutch Immunisation Programme and persons who belong to a religion from which it is known that vaccination is refused research has to be carried out in municipalities with a low vaccin coverage such that the number of persons in these subgroups will increase.