Timing of the Mode Switch

I just got back from JSM where I presented the results of an experiment that varied the timing of the mode switch in a web-telephone survey. I'm not going to talk about the results of the experiment in this post, just the premise.

The concern that motivated the experiment had to do with the possibility that longer delays before switching modes could have adverse effects on response rates. This could happen for several reasons.

• If there is pre-notification, then the effect of the prenote on response to the second mode might be reduced with longer delays before switching. 
• If the first mode is annoying in some way, it can diminish the effectiveness of the second mode.

The latter case is particularly interesting to me. It points to the ways that different treatment sequences can have different levels of effectiveness. We saw an impact like this in an experiment we did of two sequences of modes for a screening survey. The two sequences functioned about the same in terms of response to the screening survey. But among the eligibles, one of the screening sequences led to higher response rates on a follow-up, in-depth interview.  Lynn  found a similar interaction in a panel survey, where earlier modes were related to response at later waves.

I'm interested in these sorts of interactive effects between treatments as it makes it seem that we should be thinking about the sequence of treatments. That is, the full context of each component of the sequence.