However, it is possible that those individuals whose health deteriorates more markedly over time will discontinue study participation, biasing findings towards healthier participants.
Although there was little difference in background characteristics between these participants and those who did not undergo these studies, participation bias cannot be excluded.
In the Interphone study, 4 participation bias had been postulated as an explanation for the overall reduced risk for glioma and meningioma.
Furthermore, five out of six previous studies of participation bias, among volunteers in medical trials have shown that participants in screening programs, in general, have a more robust personality and less psychopathology compared with smokers in the general population.
Concerns regarding inability to refuse study participation, racial biases affecting study design and execution, and ambiguity with regard to how community input would be used in study decisionmaking were raised in several 2-way communications.
Those who responded to the headache questions were younger, were more likely to be women and had higher socioeconomic status than nonresponders On the other hand, the wide scope of the HUNT studies makes participation bias with specific relevance to headache less likely.
The nonrandom selection of households for monitoring may tend to overestimate the likelihood of fugitive emissions to the extent that study participation may be biased to households with higher emissions.
The purpose of the non-responder study was to detect participation bias, which, according to this study, led to an over-estimation of the prevalence of headache yesterday.
This instrument examines four potential sources of bias: study participation, study attrition, confounding variables and measurement of outcomes.
The present study, free from any participation bias, supports the previous international findings of an increase in AL incidence close to VHV-HVOL.
We have clearly shown that past screening attendance among women who accepted to join our study was affected by participation bias.
