Measuring change over time is one of the main purposes of longitudinal surveys. With an
increase in the use of web as a mode of data collection it is important to assess whether the
web mode differs from other modes with respect to the number of changes and events that
are captured. We examine whether telephone and web data collection modes are comparable
with respect to measuring changes over time or experiencing events. Using experimental
data from a two-wave pilot of the Swiss Household Panel, we investigate this question
for several variables in the domain of work and family.
We find differences for the work-related variables, with web respondents more likely to report
changes. These differences do not disappear once the socio-demographic composition
of the sample is taken into consideration. This suggests that these differences are not driven
by observed different characteristics of the respondents who may have self-selected into
one or the other mode. Contrary to work-related variables, a termination of a relationship
was more common in the telephone group. This shows that one mode does not necessarily
measure more change or events than another; it may depend on the variable in question.
In addition, the difference in the protocol mattered: a web respondent in a household that
participated fully by web sometimes differed from a web respondent in a household that
had a household interview by phone. Nonetheless, the telephone group differed more from
the various web protocols that the web protocols among themselves.
With more household panel surveys introducing web questionnaires in combination with
more traditional face-to-face and telephone interviews, this study adds to our understanding
of the potential consequences of mixing modes with respect to longitudinal data analysis.