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help for ^mwstati^                                               (STB-36: sg69)
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Immediate Mann-Whitney Statistic
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    ^mwstati^ 1 2 [3], ^pp^ ^pr^oportion ^m^atched ^i^ndependent


Description
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Gives the Mann-Whitney statistic ("probability that a randomly selected member 
of one group will have a better result than a randomly selected member of the 
other group") for pre-post studies, comparisons of proportions, matched pairs
t tests, and independent groups t tests.


Options
-------

^pp^, pre-post studies, ^1^ is number improved, ^2^ is total number.

^proportion^, comparisons of proportions, ^1^ is proportion of "treatment" 
     group who improve, while ^2^ is proportion of "control" group who improve.

^matched^, matched pairs t tests, ^1^ is average difference, while ^2^ is 
     standard deviation of differences.

^indenpendent^, independent groups t tests, ^1^ is difference of means; ^2^ is 
     variance for one group, while ^3^ is variance for other group.

Note that this statistic is given at the very end of @ranksum2@ for a
nonparametric comparison (via the ranksum test)

Although four options are listed above, they are not really optional in the
sense that one (1) (and only one) of them must be used.


Remarks
-------

In addition to its use in helping to interpret statistical results, this
statistic can also be used, with caution, to "adjust" the results from studies
that are of lower quality than desired.  For example, Colditz, et al. (1989)
suggest that studies that use sequential assignment, rather than random
assignment, should have their Mann-Whitney statistics reduced by 0.15 and that
non-double-blind randomized studies should be decreased by 0.11.  Another
example (Colditz, et al., 1988a) is that when there is a standard therapy but
the control group is a placebo group, the Mann-Whitney statistic should be 
decreased by 0.10!

The formulas used are from Colditz, et al. (1988b); in that article they also
present a formula for obtaining a combined score across several measure,
weighting each the inverse of their standard deviations.  This requires the
sample size for each group.


Author
------

     Richard Goldstein
     Qualitas, Inc.
     richgold@@netcom.com


References
----------

Colditz, G. A., J. N. Miller, and F. Mosteller. (1988a). The Effect of Study 
Design on Gain in Evaluations of New Treatments in Medicine and Surgery. Drug
Information Journal. 22, 343-352.

Colditz, G. A., J. N. Miller, and F. Mosteller. (1988b). Measuring Gain in the
Evaluation of Medical Technology. International Journal of Technology
Assessment. 4, 637-42.

Colditz, G. A., J. N. Miller, and F. Mosteller. (1989). How Study Design 
Affects Outcomes in Comparisons of Therapy, I: Medical. Statistics in 
Medicine. 8, 441-54.


Also See:
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    STB:  STB-36 sg69
on-line:  @ranksum2@ (if installed), @overlap@