Optimizing the design of web-based questionnaires--experience from a population-based study among 50,000 women.
BACKGROUND
Web-questionnaires are an important tool for future epidemiological research because these allow for rapid and cost-efficient assembly of self-reported information on risk factors and health outcomes. However, to achieve high response rates it is essential to accommodate factors that prevent drop out and so insure validity of future studies. We aim to study how socio-demographic variables as well as design issues such as the ordering and level of difficulty (Easy-to-hard vs. Hard-to-easy) of questions in a web-questionnaire affects the probability of drop out and non-response.


METHODS
In 2003 we invited 47,859 women participating in an ongoing prospective study to a follow-up using a web-based mode. Two versions of the questionnaire existed, varying in level of difficulty (Easy-to-hard vs. Hard-to-easy). We report drop out (proportion non-completers) between groups defined by level of difficulty and estimated adjusted risk differences.


RESULTS
The drop out differs significantly depending on the order of the questions in the web-questionnaire. The socio-demographic pattern among lurkers (participants that enter, start responding to, but do not complete a web-questionnaire) differs from that among completers of web-questionnaires.


CONCLUSIONS
An additional 6% units of completers--persons initiating and completing the questionnaire--can be obtained by considering the ordering of questions. A group uniquely identified in web-surveys, as lurkers are potentially easier to persuade to complete an already started web-questionnaire compared to a non-responder. Lurkers thus constitute a unique opportunity of decreasing the drop out rate and therefore merit future research.
Ekman
Alexandra
A
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Nobels väg 12A, SE-171 77, Stockholm, Sweden. Alexandra.ekman@ki.se
Klint
Asa
A
Dickman
Paul W
PW
Adami
Hans-Olov
HO
Litton
Jan-Eric
JE
D015331:Cohort Studies; D032882:Comprehension; D005260:Female; D006801:Humans; D020407:Internet; D010352:Patient Dropouts; D011446:Prospective Studies; D011795:Surveys and Questionnaires / Q000592:standards*; D013548:Sweden