Differences in General Health of Internet Users and Non-users and Implications for the Use of Web Surveys

Rainer Schnell, Marcel Noack, Sabrina Torregroza


Web surveys have become popular in many fields of research. To
compensate persisting undercoverage and nonresponse problems of
web surveys, weighting strategies are used. However, the underlying
assumptions of weighting are rarely tested. If the probability of missing
data depends on the missing data itself (missing not at random,
MNAR), no standard weighting method will correct for nonresponse
or undercoverage bias. We postulate a MNAR selection effect due to
health conditions. Using real data from large scale non-internet surveys
in different countries (European Social Survey (ESS), n 55; 000,
Behavioral Risk Factor Surveillance System (BRFSS), n 492; 000),
large differences in general subjective health between Internet users
and non-users can be observed. Weighting by calibration on age, gender, ethnic background, urban residence, education and household income does not eliminate the observed health differences. Therefore,
the underlying missing data mechanism might be considered as an example of MNAR. If this holds, no weighting strategy will be able to
eliminate health bias in web surveys.


MNAR; Bias; ESS; BRFSS; Weighting; Calibration

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DOI: http://dx.doi.org/10.18148/srm/2017.v11i2.6803

Copyright (c) 2017 Rainer Schnell, Marcel Noack, Sabrina Torregroza

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