Abstract
To investigate the effect of a change from the telephone to the web mode on item nonresponse in panel surveys, we use experimental data from a two-wave panel survey. The treatment group changed from the telephone to the web mode after the first wave, while the control group continued in the telephone mode. We find that when changing to the web, “don’t know” answers increase moderately from a low level, while item refusal increases substantially from a very low level. This is the case for all person groups, although socio-demographic characteristics have some additional effects on giving a don’t know or a refusal when changing mode.