power analysis and sample size

[bill higgins <bill_higginsus@xxxxxxxxx>]

We are planning to do a study using case records.  We
want to understand the probability of running away as
it related to parental visits.  We have little
research knowledge in our office so could someone help
us resolve the issue of power and sample size.  I have
the G-power program which was a free download, but we
are not sure how to use it.  We were thinking of using
75 cases which will take a lot of time, but is this
enough?  How many is enough?  What exactly is power?  

Bill


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