Does anyone know of a sampling formula to use for a proportion when
you have 'clusters' of dependent cases in the population?
I have to calculate a proportion of certain criteria that are met upon
inspection of records in an agency. The problem is that a single
employee may complete 10-20 records, therefore the assumption of
independence of cases is blown. Therefore, I can't use the old
tried-and-true sampling formula:
2
t PQ n=sample size
---- t=t-value for desired confidence level
2 (e.g. 1.96 for 95%)
d P=proportion with trait in population
n= -------------------- (if unknown, 50% most conservative)
2 Q=1-P
1 t PQ d=desired precision
1 + -- * ( ----- - 1 ) (confidence int = proportion +-d)
N 2 N=population size
d
which is used for, like, political polls where every case is an
independent person.
What do I do?
Thanks much!
Scott Edwards
Tallahassee, FL
.
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