Table 5

Relative efficiency of ANCOVA and Mann-Whitney combining all sample sizes. Values less than 1 indicate greater power of ANCOVA; greater than 1 indicates superiority of Mann-Whitney.

Distribution
Correlation between baseline and post-treatment score



0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9

Moderate positive skew: shift
0.9342
0.9257
0.8707
0.8532
0.8569
0.9030
0.9447
0.9538
0.9963
Moderate positive skew: ratio
1.1560
1.1300
1.1074
1.0800
0.8170
0.8656
0.9065
0.9231
0.9720
Moderate negative skew: shift
0.9392
0.9058
0.8837
0.8444
0.8799
0.9114
0.9421
0.9593
0.9885
Moderate negative skew: ratio
1.1766
1.1946
1.1467
1.0980
0.8851
0.9319
0.9671
1.0241
1.0390
Uniform: shift
0.9492
0.9170
0.8869
0.8480
0.8586
0.8977
0.9281
0.9723
1.0021
Uniform: ratio
0.9575
0.9384
0.8862
0.8499
0.8604
0.8849
0.9213
0.9467
0.9895
Extreme negative skew: shift
1.4019
1.3718
1.3339
1.3045
0.8987
0.9425
0.9475
0.9405
0.9345
Extreme negative skew: ratio
1.6914
1.6185
1.6101
1.5835
1.0153
1.0367
1.0247
1.0344
1.0062
Normal: shift
0.9700
0.9393
0.9142
0.8445
0.8372
0.8840
0.9065
0.9485
0.9734
Normal: ratio
0.9551
0.9506
0.9126
0.8791
0.8536
0.8859
0.9072
0.9293
0.9654

Vickers BMC Medical Research Methodology 2005 5:35   doi:10.1186/1471-2288-5-35