Mary has given you a correct answer, play with the format. In my case I do not define any format because the ODS tables will provide you the right p-values if they are very small, as long as you transfer to your tables and remove the sas format.

For example I capture a table with ods output SAStablename=mytablename;

and when I refer to my table name I use before the set statement the following, which removes the SAS format default for the ProbF.

format ProbF ;

In regard to the such low p-values. They are meaningful when the p (number of variables tested) is large. For example one can apply 1Million independent tests, and by rules of probabilities one would expect 5% false positives by chance. Therefore in the Genetic analysis and in other sciences are developed multiple corrections (see proc multtest). The simples and the most conservative one is Bonferroni test (when alpha=0.05) a family wise alpha=0.05/(# of tests=1M) => 5e-8.

HTH,

Aldi

Mary wrote: > To answer the question; save the result in ODS and then you can set a > format > of the resulting value however you want; > it is a format question rather than a value question. I haven't actually > tried this big a format in SAS but know that it saves it, as > I can reformat it over in Excel so I know it does save the decimals. > > ods select ChiSq; > data chisq_set; > informat chi_square 20.14 format chi_square 20.14 table $256.; > stop; > run; > ods output chisq=chisq_set; > proc freq data=set2; > tables amd_flag * &snp/chisq nocol norow nopercent; > title &snp; > run; > > data chisq_set; > informat chi_square 20.14 format chi_square 20.14 table $256.; > set chisq_set; > where Statistic='Chi-Square'; > table=trim(substr(table,index(table,'*')+1,length(table))); > chi_square=prob; > keep table chi_square; > run; > > To answer Dale's question, WHY?, this may be due to many thousands of > multiple tests, for instance in Genetics. > > In my field, Ophthalmology Macular Degeneration, a major paper was > published > in which all but 2 of over 116,000 SNPs > were discarded: > > Complement factor H polymorphism in age-related macular degeneration. > Klein et al. Science. 2005 Apr 15;308(5720):385-9. > > In this, they set a Bonforroni acceptance level of 10 -7. > > http://www.sciencemag.org/cgi/content/full/308/5720/385 > > "Single-marker associations. For each SNP, we tested for allelic > association > with disease status. To account for multiple testing, we used the > Bonferroni > correction and considered significant only those SNPs for which P < > 0.05/103,611 = 4.8 x 10-7. This correction is known to be conservative > and > thus "over-corrected" the raw P values (14). Of the autosomal SNPs, only > two, rs380390 and rs10272438, are significantly associated with disease > status (Bonferroni-corrected P = 0.0043 and P = 0.0080, respectively) > (Fig. > 1A). " > > > > -Mary > > > > > > > > ----- Original Message ----- > From: baxtefer@GMAIL.COM > To: SAS-L@LISTSERV.UGA.EDU > Sent: Monday, November 10, 2008 3:28 PM > Subject: Probchi and large Chi-squares > > > This might be a really stupid question... > I need to get the exact probabilities associated with a number of > large Chi-Square values (i.e. >100, 1 DF) > using > P = 1-Probchi(ChiSq,1); > can give me values of P down to around 1E-16, but anything less than > that gets represented as 0. > Is this a real issue or am i dealing with a number formatting problem? > > Thanks in advance!

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