Nonresponse bias in EC Respiratory Health Survey in Italy

Abstract

In the three Italian centres involved in the European CommunityRespiratory Health Survey (ECRHS), prevalence of asthma-like symptoms was assessed through a mailback questionnaire. Since the nonresponse rate was not negligible, ranging 10-18%, we investigated whether nonresponse bias affected the results and, if so, whether the bias could be eliminated from the final estimates of prevalence.A screening questionnaire was sent by mail to 7,000 randomly selected subjects 20-44 yrs of age, and nonresponders were contacted again by phone. Additional information was collected on a subsample of the respondents through a clinical interview.A logistic regression analysis showed that, except for one symptom (awakening for coughing), symptom prevalence significantly decreased from the first to the subsequent contact, when controlling for age, sex, centre and season of interview. The decrease in symptom prevalence was largely independent of smoking habits and socioeconomic status, and was seemingly caused by a symptom-related selfselection. When correcting results according to a linear regression model, observed estimates appeared to be slightly overestimated, by 4-10%. A simulation with the Italian data showed that the bias increased steeply at nonresponse rate higher than 30%, a situation quite common in asthma surveys.In conclusion, nonresponse bias affects the results of ECRHS in Italy, slightly inflating prevalence estimates. To make reliable comparisons on international data in the presence of different nonresponse rates, a correction of the observed prevalence seems necessary.

Prevalence of respiratory symptoms, bronchial hyperresponsiveness and atopy among adults: west and east Germany

“…There was a decrease in symptom rates between Stage I and II for several symptoms, e.g. wheeze and hay fever, as has been described in other centres of the EC Respiratory Health Survey [48]. This effect did not differ significantly between Hamburg and Erfurt (data not shown).…”

COPD prevalence and its association with occupational exposures in a general population

“…Such response patterns are frequently seen in epidemiological studies [30]. There was no evidence of bias in favour of those most likely to have been particularly affected by workplace exposure.…”

Classification of personal exposure to radio frequency electromagnetic fields (RF-EMF) for epidemiological research: Evaluation of different exposure assessment methods

“…It can be introduced if an exposure assessment method requires active participation from potential study participants, and it is expected to be specifically pronounced if a large effort for study participants is involved. In this case, a substantial part of the study participants might refuse to participate, which may be of major of concern if participation is related to both health and exposure status (Bakke et al, 1990;de Marco et al, 1994;Röösli, 2008). Collecting exposimeter measurements in combination with diary data is likely to introduce participation bias because of the large effort required for study participants.…”