On 7 Ean 2010, at 09:41, Miranda Kim wrote:
For example, previous research on a given association yields a
correlation coefficient 0.41 with p-value 0.131 and n=15.
Initially I was looking at what sample size n would be required to
have
90% power to detect a correlation coefficient 0.41 using a test at the
5% level of significance.
The question is not what the actual correlation is likely to be, but
the size of the smallest correlation which is of real-life importance.
This should be the basis of your power calculation. In medicine we
refer to the smallest effect which is of real life importance as the
smallest clinically significant difference. I imagine that it has
other names in other disciplines (any volunteers?).
I see this confusion a lot as an ethics committee reviewer.
Ronan Conroy
=================================
[email protected]
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)
http://rcsi.academia.edu/RonanConroy
P Before printing, think about the environment
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
