selection bias?

[bill higgins <bill_higginsus@xxxxxxxxx>]

I am evaluating the effects of a particular parenting
program in Maine.  Unfortunately these parents self
selcted into this program (that is, their
characterisitcs helped place them in this program). 
How can I correct for this problem in my statistical
analyses?  I am not a researcher by training - so
perhaps this is an easy question.  Examples and
references would help.

Thanks,

Bill Higgins

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