FAQ/power/pPowN - CBU statistics Wiki
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An on-line power calculator is available.

Computes total sample size needed for testing prop=const where prop and const are observed and expected (constant) proportions respectively and alpha is the (two-tailed) type I error for a given power. A calculator is available in a spreadsheet.

[COPY AND PASTE THE SYNTAX BELOW INTO A SPSS SYNTAX WINDOW AND RUN; SET DATA AS DESIRED]

```DATA LIST free
/prop const alpha power.
BEGIN DATA.
0.45 0.5 .05 .85
0.55 0.5 .05 .85
END DATA.

set errors=none.
define propn (!pos !tokens(1)
/ !pos !tokens(1)
/ !pos !tokens(1)
/ !pos !tokens(1)).
COMPUTE #POW = !4.
compute #conf = 1-!3.
compute #lc3 = 1.
compute #ind=0.
compute #chisq = 3.
comment COMPUTE #LC1 = 2.000.
COMPUTE #chisq1 = ((!1-!2)**2)/(!2*(1-!2)).
COMPUTE #CUMF2 =  1 - NCDF.CHISQ(IDF.CHISQ(#conf,1),1,#CHISQ).
compute #diff=1.
SET MXLOOPS=40000.
LOOP IF (#DIFF GT .00005) .
+       DO IF (#CUMF2 LT #pow) .
+               COMPUTE #LC3 = #CHISQ.
+               COMPUTE #CHISQ = (#chisq + 0.001).
+               COMPUTE #CUMF2 =  1 - NCDF.CHISQ(IDF.CHISQ(#conf,1),1,#CHISQ).
+       ELSE .
+               COMPUTE #LC1 = #chisq .
+               COMPUTE #chisq = (#chisq + #LC3)/2 .
+               COMPUTE #CUMF2 =  1 - NCDF.CHISQ(IDF.CHISQ(#conf,1),1,#CHISQ).
+       END IF .
+       COMPUTE #DIFF = ABS(#CUMF2 - #pow) .
END LOOP .
compute ntot = #chisq/#chisq1.
if (ntot-trunc(ntot) gt 0.5) #ind=1.
if (#ind eq 0) ntot=trunc(ntot)+1.
if (#ind eq 1) ntot=rnd(ntot).
EXECUTE .
compute prop=!1.
compute const=!2.
compute alpha=!3.
compute power=!4.
formats ntot (f7.0) alpha (f5.2) prop (f5.2) const (f5.2) power (f5.2).
variable labels ntot 'Sample Size Required' /alpha 'Alpha' /prop 'Observed Proportion' /const 'Constant' /power 'Power'.
report format=list automatic align(center)
/variables=ntot alpha prop const power
/title "Sample Size required for a one sample binomial test" .
!enddefine.

matrix.
get m /variables=prop const alpha power  /missing=omit.
compute prop=make(1,1,0).
compute const=make(1,1,0).
compute alpha=make(1,1,0).
compute power=make(1,1,0).
compute prop=m(:,1).
compute const=m(:,2).
compute alpha=m(:,3).
compute power=m(:,4).
end matrix.
propn prop const alpha power.```

None: FAQ/power/pPowN (last edited 2013-03-08 10:17:12 by localhost)