On Thu, Nov 8, 2012 at 6:22 PM, Glynn Clements <[email protected]> wrote: > > Paulo van Breugel wrote: > >> Just wondering, if it is implemented in r.regression.series, would it be >> very difficult to port to r.series? Or do the two things function different >> internally? > > It could probably be added to r.series quite quickly if someone was > willing to provide definitions for "t-value" and "p-value".
The t-value of a simple linear regression can be calculate with t = sqrt(Rsq) * sqrt((n - 2) / (1 - Rsq)); Rsq = R squared or coefficient of determination (r.series method=detcoeff) n = sample size This formula is used by r.regression.multi and in some modules in GRASS 5 that also do multiple regressions. The p-value would then be the cumulative probability of observing t according to Student's t-distribution for given n. I think somewhere in GRASS is a function to calculate p for n = inf (normal distribution). Maybe somewhere hidden there is also a function for small n? Markus M _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
