The main differences lie with study design
and execution using Web 2.0 technologies rather than
conventional paper and pencil and in-person tools and
with difficulties in designing and maintaining study rigor.
These issues emerge as evaluators consider design issues
such as whether an experimental or quasi-experimental
design will be used, how study participants will be recruited
or randomized, how survey design can yield best response
rates, and how to control for the influence of other interventions and confounding factors that might affect study
results. Attrition, when participants stop usage or are
lost to follow-up, has also been identified as a fundamental issue for evaluation of online interventions
(Eysenbach, 2005).