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help for ^metap^                             (STB-49: sbe28)
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Meta-analysis of p-values
-------------------------

	^metap^ pvar [^if^ exp] [^in^ range] [^, e(^#^)^]


Description
-----------

^metap^ provides combination of p-values from each study. The user provides the 
one-tail p-values as ^pvar^. 

If you have a dataset which contains data for all studies, then the @byvar@
command (STB-27) can be used to derive the p-values for the individual studies.
For example:

   . ^sort study^
   . ^byvar study, coef(group) se(group) generate:^
   . ^quietly poisson cases group, e(pyrs)^
   . ^sort study^
   . ^qui by study: keep if _n==1^
   . ^rename _C_1 logrr^
   . ^rename _S_1 se^
   . ^generate pvar=norprob(-logrr/se)^
   . ^metap p^

Alternatively, the @collapse@ or @for@ commands may be useful.


Option
------

^e(^#^)^ combines the p-values using Edgington's (Edgington 1972a, 1972b) methods. 
Here, two alternatives are available: ^a^ additive method based on the sum of 
probabilities, this method is suggested to combine a small number of studies, 
producing similar results as Fisher's method. ^n^ normal curve method based on 
the contrast of the p-value average, this methods is suggested to combine a 
large number of studies. By default Fisher's (Fisher 1932) method is used. 


Examples
--------

   . ^metap pvar^
   . ^metap pvar, e(a)^
   . ^metap pvar, e(n)^


Author
------

    Aurelio Tobias
    Statistical Consultant
    Madrid, Spain
    email: bledatobias@@ctv.es


References
----------

Edgington, E.S. (1972a). An additive method for combining probability values 
from independent experiments. Journal of Psychology, 80: 351-363.

Edgington, E.S. (1972b). A normal curve method for combining probability values
from independent experiments. Journal of Psychology, 82: 85-89.

Fisher, R.A. (1932). Statistical Methods for Research Workers 4th ed. London:
Oliver & Boyd.


Also see
--------

    STB:  STB-49 sbe28
On-line:  help for @byvar@, @collapse@, @for@, @meta@ (if installed), @metareg@ 
          (if installed), @metabias@ (if installed), @metacum@ (if installed), 
          @galbr@ (if installed), @metainf@ (if installed)