Does non-responder bias have a significant effect on the results in a postal questionnaire study?
OBJECTIVE
In epidemiological questionnaire studies results can be influenced by non-responder bias. However, in respiratory epidemiology this has been analysed in very few recently published papers. The aim of our paper is to assess if the results found in our previous postal questionnaire study in an adult population in Northern Finland were biased by non-response.


METHODS
A random sample of 385 persons from the 1,284 non-responders in a previous postal questionnaire study was examined. The same questionnaire as in the original study was again mailed to these persons, and those still not answering were contacted by phone.


RESULTS
Totally 183 complete answers (48%) were collected. Lack of interest (56%) and forgetting to mail the response letter (22%) were the most common reasons to non-response. Typical non-responders were young men and current smokers who less frequently reported respiratory symptoms in exercise and asthma than the responders in the original study. Answers collected by phone gave for some questions higher prevalence rates than postal answers.


CONCLUSIONS
Firstly, in this population the response rate (83.6%) in the original study was high enough to provide reliable results for respiratory symptoms and diseases, only the prevalence of current smoking was biased by non-response. Secondly, the methods used for collecting responses in a non-response study may influence the results.
Kotaniemi
J T
JT
Department of Pulmonary Medicine, Päijät-Häme Central Hospital, Lahti, Finland. jyrki.kotaniemi@phks.fi
Hassi
J
J
Kataja
M
M
Jönsson
E
E
Laitinen
L A
LA
Sovijärvi
A R
AR
Lundbäck
B
B
D000328:Adult; D000368:Aged; D015982:Bias; D016009:Chi-Square Distribution; D004812:Epidemiologic Methods; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011177:Postal Service; D015995:Prevalence; D012140:Respiratory Tract Diseases / Q000453:epidemiology*; D012307:Risk Factors; D011795:Surveys and Questionnaires