## Exact Power [R for BE/BA]

Dear all,

I made an investment and was able to compare results from R with the current version 7 of nQuery Advisor:*
 +======+=====+===========+========+==========+ |  GMR |  n  |  R-code   | nQuery Advisor 7  | +------+-----+-----------+--------+----------+ | 0.85 | 134 | 0.8017723 | 80.17  | 80.17722 | | 0.90 |  38 | 0.8154940 | 81.54  | 81.54941 | | 0.95 |  20 | 0.8346802 | 83.46  | 83.46802 | | 1.00 |  16 | 0.8331980 | 83.32  | 83.32001 | | 1.05 |  18 | 0.8001854 | 80.01  | 80.01854 | | 1.10 |  32 | 0.8100682 | 81.00  | 81.00682 | | 1.15 |  72 | 0.8042181 | 80.42  | 80.42180 | | 1.20 | 294 | 0.8019247 | 80.19  | 80.19246 | +======+=====+===========+========+==========+

nQuery requires sqrt(MSE) rather than CV as input = sqrt(ln(CV²+1)). The maximum precision is 6 decimal places. Therefore 0.1980422 rather than the value in full precision (0.1980422004353650284627675024887) like in R is used. But you see this value only if clicking the respective cell; both displayed and printed is 0.198042. nQuery gives power in percent with a maximum number of two decimal digits. That's a pity and values in the first column were the best one could get (display/print). If clicking in each cell power is given in percent to 5 decimal digits (7 significant digits); second column. It's clear that results are not rounded, but truncated. This looked weird first, but at least for power it makes sense.
Values agree nicely with the exception of a small discrepancy at GMR=1 (83.31980% vs. 83.32001%).
If I recall it correctly Dieter Hauschke wrote something about numerical problems in power estimation at T/R=1 in one of his papers.

I love validating software.

• Janet D Elashoff
Statistical Solutions, Cork, Ireland (2007)

Cheers,
Helmut Schütz

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