One more thing to consider. As Rich Ulrich alluded to, any effort like this is going to have false positives (investigating innocent people). It is also going to have false negatives (ignoring fraudulent transactions). There are costs associated with each. So you need to have data on which transactions end up being "normal" and which ones indicate problems (fraud, stolen credit card, and so forth). Then compute sensitivity and specificity and balance these according to the respective costs.
This is not an easy thing to do, but it is the only way to assess whether your procedure works well or not.
Good luck!
Steve Simon, [EMAIL PROTECTED], Standard Disclaimer.
The STATS web page has moved to
http://www.childrens-mercy.org/stats.
