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Simulation of Limits

In my last post, I advocated against truncating effort. In this post, I'm going to talk about doing just that. Go figure.

We were discussing call limits on a project that I'm working on. This is a study that we plan to repeat in the future, so we're spending a fair amount of time experimenting with design features on this first wave.

There is a telephone component to the survey, so we've been working on the question of how to specify the calling algorithm and, in particular, what if any ceiling we should place on the number of calls.

One way to look at it is to look at the distribution of final outcomes by call number -- sort of like a life table. Early calls are generally more productive (i.e. produce a final outcome) than late calls. You can look at the life table and see after which call very few interviews are obtained. You might truncate the effort at that point.

The problem is that simulating what would happen if you place a ceiling on the number of calls isn't the same thing as actually placing a limit on calls. Especially in a phone lab. In the phone lab, if you don't do something (place a call on a case over the limit), then you are going to call a case that wouldn't have otherwise been called. Even if there are fewer hours of interviewing, this is likely to change how the calls are distributed over time.

Telephone labs are a complex system. Sometimes it feels like every time you turn a knob to change one setting, something unexpected happens somewhere else in the system. It makes for an interesting problem.


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