Field examination stages
The field investigation had four stages: pre-questionnaire, health examination, re-examination and report on non-participants.
Pre-questionnaire
The pre-data was gathered with a questionnaire consisting of 156 questions, which was sent alongside the invitation to be completed at home about two weeks before the scheduled examination day. With the questionnaire, information was retrieved about the participant´s sociodemographic factors, health behavior, medication, diseases and their treatment.
Health examination
On the research site, the questionnaire was checked and the person participated in the health examination which consisted of the following measures in the order given:
- Checking the basic questionnaire and completion of the interviews
- Measurement of blood pressure and pulse, registering the length of fasting
- Taking urine sample
- Measurement of resting ECG
- Taking fasting blood sample
- Measurement of height and weight and giving glucose dose for 1-hour glucose tolerance test
- Coronary interview
- Measurement of miniature chest X-ray
- Measurement of skinfolds
- Drawing blood sample for 1-hour glucose tolerance test
Re-examination
About 2-4 months after the health examination, the participant was invited to a re-examination to check the results, if something abnormal was found. On average one third of the participants of the baseline health examination was invited to the re-examination.
Participants, who were detected some of the following in the baseline health examination, were invited to the re-examination (Method folder 2.20):
- those with atypical findings suggesting trouble in heart, circulation, glucose metabolism, lung and kidney function, hematology or thyroid gland. The criteria were high blood pressure, high blood lipids, cardiovascular symptoms, ECG or miniature chest X-ray finding, high blood glucose, high blood creatinine, urine findings, high or low hematocrit, and high or low blood thyroxine
- those who belonged to the repeatability sample for quality control
- those with missing information in important measures in the baseline examination such as resting ECG or chest miniature X-ray measurement
- those not attending the baseline survey
Additional examinations (i.e. coronary interview, the measurement of the blood pressure, urine examination, ECG measurement, large picture chest X-ray, blood measurements, urine measurements, measurement of height and weight) and a clinical examination (regarding heart and circulation, the thyroid gland, kidney and lungs) were carried out in the re-examination depending on the findings of the baseline study. For the repeatability sample all the measures of the baseline survey were carried out apart from miniature X-ray on the chest
2.20 Re-examination selection criteria (in Finnish)
Report on non-participants
For the non-participants of the health examination, sociodemographic information, some information regarding health and the reasons for non-attendance were gathered alongside the re-examination (AU05) and with a mailed questionnaire (AU27). The registry data regarding them has been linked to the database.
AU05 Basic questionnaire (non-participants)
AU27 Non-participant questionnaire (mailed)
Quality control
The quality of the data was ensured by a comprehensive set of instructions and training, by following the actions in the field examination, by observing the quality and by calibrating and maintaining the equipment (ECG device scale and blood pressure meter). In addition quality of the data was estimated through different experimental designs. The collected data was checked both in regard to missing data and possible inconsistencies between the data.
Observer-based population distributions were continuously followed. Also parallel and repeated measurements were evaluated. Based on these results, it was pursued to improve the measures as an additional training. Regularly, often daily, calibration of the instruments was carried out. The functioning of the ECG device was checked with a simulator, the weight scale was calibrated with weights, the blood pressure observers listened regularly to the Rose tape (Korotkoff sounds) and their recordings were followed.
In the laboratory of the Finnish Mobile Clinic, standard valid quality control methods were used. These were calibration of the instruments, repeated measurements and analyzing of both the laboratory’s own and extraneous reference samples. Reference values were obtained from the Finnish quality control system (Kliinisten laboratoriotutkimusten laaduntarkkailu Oy) and the US CDC.
To assess the quality of the methods, various specific study designs were constructed. The data of the biological repeatability consisted of a 10 % random sample of the participants in the baseline survey, who were invited to the re-examination survey for repeated measurements and interviews. For instance, the repeatability of the basic questionnaire (AU02), coronary interview (AU19, AU73), dietary interview (AU24) and the resting ECG measurements were assessed. Also experiments for the evaluation of the analytical repeatability were designed. The analytical repeatability was evaluated e.g. for coding of the disease and occupational classification, the ECG classification, anthropometric measurements and blood pressure measurement. Furthermore, possible systematical biases were studied in designs evaluating the agreement between the results of the field observer and those of reference observers. Additionally, a long-term follow-up of the field staff blood pressure was carried out. Based on it, the stability of the measurement can be assessed.
AU02 Basic questionnaire B, quality control (in Finnish)
AU19 Coronary interview, baseline examination (in Finnish)
AU24 Dietary interview
AU73 Coronary interview, re-examination (in Finnish)
