Dear R-users Please excuse me if this topic has been covered before, but I was unable to find anything relevant by searching
I am currently doing a comparison of two biological variables that have a highly significant linear relationship. I know that the p-value of linear regression is not so interesting in itself, but this particular value does raise a question. How does R calculate (extremely low) p-values for linear regression? For my data I got a p-value on the order of 10^-9 and a reviewer commented on this. I tried to run the same analysis in both SAS and Sigmastat to be sure that I was doing it right, but both these programs only return a p-value of p < 0.0001 Since I am unable to reproduce my results in another statistics program, it would be nice to be able to explain this unusally low p-value to the reviewers. This "problem" can be illustrated with the following made-up data: x_var<-c(0.149,0.178,0.3474,0.167,0.121,0.182,0.176,0.448,0.091,0.083,0.090,0.407,0.378,0.132,0.227,0.172,0.088,0.392,0.425,0.150,0.319,0.190,0.171,0.290,0.214,0.431,0.193) y_var<-c(0.918,0.394,0.131,0.9084,0.916,0.934,0.928,0.279,0.830,0.927,0.964,0.323,0.097,0.914,0.614,0.790,0.984,0.530,0.207,0.858,0.408,0.919,0.869,0.347,0.834,0.276,0.940) fit<-lm(y_var~x_var) > summary(fit) Call: lm(formula = y_var ~ x_var) Residuals: Min 1Q Median 3Q Max -0.39152 -0.06027 0.00933 0.10024 0.22711 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 1.18696 0.06394 18.562 3.90e-16 *** x_var -2.25529 0.24788 -9.098 2.08e-09 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Residual standard error: 0.1503 on 25 degrees of freedom Multiple R-squared: 0.768, Adjusted R-squared: 0.7588 F-statistic: 82.78 on 1 and 25 DF, p-value: 2.083e-09 With kind regards, Sindri Traustason ----- ----------------------------------------- Sindri Traustason Glostrup Hospital Ophthalmology Research Dept. Copenhagen, Demark -- View this message in context: http://r.789695.n4.nabble.com/Calculation-of-extremely-low-p-values-in-lm-tp4651823.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.