Friday, July 13, 2012

Case-level Phases

Groves and Heeringa conceived of design phases as a survey-level attribute. But nothing prevents us from thinking of methods for using the technique at a case-level.

In the last post, I talked about formalizing the concept of "phase capacity" using stopping rules. It might be that a similar logic could be used to formalize decisions at the case level.

For instance, a few years ago on a telephone survey we implemented two-phase sampling. We implemented the phase-boundary using a case-level rule: after a certain number of calls, you entered the second phase. There might be other ways in which stopping rules like this could be used in order to change the design at the case level.

Wednesday, July 11, 2012

Responsive design phases

In the paper on responsive design, Groves and Heeringa define "design phases." They argue that each phase has a capacity. Once that capacity has been reached, i.e. the current design has exhausted its possibilities, then a design change may be needed.

A difficulty in practice is knowing when this capacity has been reached. There are two related issues:
1. Is there a statistical rule that can be applied to define the end of the phase?
2. Can we identify when the threshold has been met immediately after it occurs, or is there a time lag?

I don't know that anyone has done much to specify these sorts of rules. I would think these are generalizations of stopping rules. A stopping rule says when to stop the last phase, but the same logic could be applied to stopping each phase. I had a paper on stopping rules for surveys a few years back. And there is another from Rao, Glickman, and Glynn. I don't know that anyone has tried this sort of extension. But I think it is an interesting idea.

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