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May 25, 2009 4:58 PM
(504 views)

Most importantly why is it different from the "usual" published formula?

for example that used on the online calculator:

http://www.stat.ubc.ca/~rollin/stats/ssize/b1.html

and detailed here:

http://www.itl.nist.gov/div898/handbook/prc/section2/prc242.htm

For example (JMP8)

with p0 = 0.1, p1 = 0.4, alpha = 0.05, 1-sided test, power = 0.8

JMP8 gives sample size = 7 (actually 6.183 - rounded up to whole number 7)

"usual" formula gives sample size = 10 (actually 9.116 - rounded up to whole number 10)

Thanks

I've changed the example so it was relevant to JMP8 (which only does 1-sided one-proportion sample size tests - or is there another way to do 2-sided?)

Message was edited by: reedme

2 REPLIES

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Aug 7, 2009 3:02 AM
(447 views)

Highlighted
JMP 8.0.1 does an Exact calculation. The 2 references you give use a normal approximation calculation. (The JMP docs say JMP is using a normal approximation but they are being updated.)

When I use 8.0.1 to calculate the sample size for the example you give, I get sample size = 13 (not 7). This agrees with the Exact calculation performed at this excellent power and sample size page: http://www.stat.uiowa.edu/~rlenth/Power/.

Michael

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Aug 27, 2009 1:33 PM
(447 views)

When I use 8.0.1 to calculate the sample size for the example you give, I get sample size = 13 (not 7). This agrees with the Exact calculation performed at this excellent power and sample size page: http://www.stat.uiowa.edu/~rlenth/Power/.

Michael