Exact Power [R for BE/BA]

posted by Helmut Homepage – Vienna, Austria, 2009-09-25 17:20  – Posting: # 4255
Views: 30,688

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.
:ponder:
I love validating software. :angry:



Cheers,
Helmut Schütz
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