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Surely there is a serious flaw in your Table II? I have checked
minimal sample sizes using: (a) nQuery Advisor v. 5; and (b) Machin D,
Campbell MJ, Fayers PM, Pinol APY. Sample Size Tables for Clinical
Studies, 2nd edn. Oxford, B;ackwell Science, 1997. I used two-sided P =
.050, power = .80 (80%), and the assumption that outcomes would be
analyzed by the uncorrected chi-squared test. Both (a) and (b) give
identical estimates.
It looks to me as if all the columns in your Table II have been
shifted to the right by 1 column. Thus, for pA = .25, pB = .35 you give n
= 1251; both (a) and (b) above give n = 329. And so forth.
John Ludbrook.
Competing interests:
None declared
Competing interests:
No competing interests
20 October 2003
John Ludbrook
Professorial Fellow
563 Canning St, Carlton North, Vic 3054, Australia
Error in Table II
Surely there is a serious flaw in your Table II? I have checked
minimal sample sizes using: (a) nQuery Advisor v. 5; and (b) Machin D,
Campbell MJ, Fayers PM, Pinol APY. Sample Size Tables for Clinical
Studies, 2nd edn. Oxford, B;ackwell Science, 1997. I used two-sided P =
.050, power = .80 (80%), and the assumption that outcomes would be
analyzed by the uncorrected chi-squared test. Both (a) and (b) give
identical estimates.
It looks to me as if all the columns in your Table II have been
shifted to the right by 1 column. Thus, for pA = .25, pB = .35 you give n
= 1251; both (a) and (b) above give n = 329. And so forth.
John Ludbrook.
Competing interests:
None declared
Competing interests: No competing interests