posted 01-07-2008 08:16 PM

Ben,That should prove very interesting.

With N=70 you may have enough to gain some preliminary figures that might begin to better inform further investigation efforts.

We are really at the onset stages of understanding base-rates and their contribution to LE officer hiring/training success.

Do you collect information about alcohol related problems? Also, how about gambling problems.

It would be interesting to see a literature search regarding the salient content for background investigation of LE candidates.

It would also be interesting to find cohorts of intermediate (3 to 8 years?) and long term LE officers (10+ years?), and perhaps even training failures and integrity failures to better evaluate the contribution of each data point to outcomes.

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Some estimates.

Observed rates of passing and failure, in mixed issues (independent RQs) exams will be subject to the multiplication rule for independent probability events. This means that we multiply the inverse of the base-rate of each of the RQs. For convenience, we'll assume the RQs to have equivalent base-rates, though this may not be the case in field situations.

Example 1: High base-rate. Assuming a LEPET exam with 4 RQs of BR = 50% = (1-.5)*(1-.5)*(1-.5)*(1-.5) = .0625 chance that any particular subject is being truthful to all RQs.

Example 2: Moderate base-rate. We'll use 15% and 3 RQs. = (1-.15)*(1-.15)*(1-.15) = 61.4% chance that any examinee is truthful to three questions of moderate BR.

Example 3: Low base-rate. Use 5% (.05) and 2 RQs. = (1-.05)*(1-.05) = 90.5% of examinee's can be expected to be truthful to two low BR questions.

Example 4: Very-low base-rate. 1% (.01) with 2 RQs = (1-.01)*(1-.01) = .98 or

The point is that if we are selecting targets that are salient or relevant to the task of predicting risk or future failure, we should be seeking higher BR behaviors that are correlated with the criterion. The trade-off is that we will find comparatively fewer and fewer persons who are being truthful to all questions.

Last week Donna posted some numbers at anti, regarding LEPET exams. I believe she indicated that approximately 70 percent of her subjects had passed. Assuming that LE applicants are not serious criminals (= moderate base-rates) and three to four questions, that would be about the right ball-park for passing rates.

r

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