```Date: Tue, 8 Nov 2005 18:36:22 +0100 Reply-To: Marta García-Granero Sender: "SPSSX(r) Discussion" From: Marta García-Granero Organization: Asesoría Bioestadística Subject: Re: Z test for proportion-Juan Albertorio In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Hi Juan, AJR> I have a question. I need to run a Z test for seek the AJR> exact P value -significance of the proportions' difference. If it is a Z test, then the p-value is asymptotic. Are you talking about getting the actual p-value, instead of just saying it's "significant' or 'non-significant'? Given the sampe sizes, I don't think you need an exact test. AJR> I already have the n's, value and standard error. My AJR> question is; Did someone knows a SPSS Syntax available were I can AJR> enter the values (show below) and calculate the exact P value? AJR> Example: AJR> N Proportion Standard Error AJR> Male 42947 15.35 0.08 AJR> Female 41294 14.36 0.07 You don't need the standard errors (they can be computed as SQRT(prop*(100-prop)/n). Try this code (tested with COMPARE2.EXE, from WinPepi statistical package): * With your data *. DATA LIST LIST/group(A6) n(F8.0) perc(F8.3). BEGIN DATA Male 42947 15.35 Female 41294 14.36 END DATA. * Method described in Chapter 6 of 'Statistic at Square One' (http://bmj.bmjjournals.com/collections/statsbk/6.shtml) *. MATRIX. PRINT /TITLE='95%CI for a difference in percentages & Z test'. GET gnames/VAR=group. GET n /VAR=n. GET perc /VAR=perc. COMPUTE sediff1=SQRT(MSUM(perc&*(100-perc)/n)). COMPUTE lower=perc(1)-perc(2)-1.96*sediff1. COMPUTE upper=perc(1)-perc(2)+1.96*sediff1. COMPUTE commonp=MSUM(n&*perc)/MSUM(n). COMPUTE sediff2=SQRT(commonp*(100-commonp)*MSUM(1/n)). COMPUTE zvalue=(perc(1)-perc(2))/sediff2. COMPUTE zsig=1-CDFNORM(ABS(zvalue)). COMPUTE labels={gnames;'Diff'}. PRINT {T(perc),perc(1)-perc(2)} /FORMAT='F8.2' /CNAMES=labels /TITLE='Percentages & Difference'. PRINT sediff1 /FORMAT='F8.2' /TITLE='SE for difference in percentages'. PRINT {lower,upper} /FORMAT='F8.2' /CLABEL='Lower','Upper' /TITLE='95% CI for the difference in percentages'. PRINT sediff2 /FORMAT='F8.2' /TITLE='SE for difference in percentages (asumming H0)'. PRINT {zvalue,zsig,2*zsig} /FORMAT='F8.3' /CLABEL='Z-value','One-tailed','2-tailed' /TITLE='Z test and significance for difference in proportions'. END MATRIX. Regards, Marta mailto:biostatistics@terra.es ```

Back to: Top of message | Previous page | Main SPSSX-L page