Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.
Y = b0 + sum(bi*Xi) + E
X = {X1, X2, ..., Xm} m = number of explaining variables Y = {y1, y2, ..., yn} Xi = {xi1, xi2, ..., xin} E = {e1, e2, ..., en} n = number of observations (cases)
Y ~ sum(bi*Xi) b0 is the intercept, X0 is set to 1
r.regression.multi is designed for large datasets that can not be processed in R. A p value is therefore not provided, because even very small, meaningless effects will become significant with a large number of cells. Instead it is recommended to judge by the estimator b, the amount of variance explained (R squared for a given variable) and the gain in AIC (AIC without a given variable minus AIC global must be positive) whether the inclusion of a given explaining variable in the model is justified.
The F score for each explaining variable allows testing if the inclusion of this variable significantly increases the explaining power of the model, relative to the global model excluding this explaining variable. That means that the F value for a given explaining variable is only identical to the F value of the R-function summary.aov if the given explaining variable is the last variable in the R-formula. While R successively includes one variable after another in the order specified by the formula and at each step calculates the F value expressing the gain by including the current variable in addition to the previous variables, r.regression.multi calculates the F-value expressing the gain by including the current variable in addition to all other variables, not only the previous variables.
The AIC value is identical to the one obtained from the R-function stepAIC() when excluding this variable from the full model. The AIC value corrected for the number of explaining variables and the BIC value (Bayesian Information Criterion) value follow the logic of AIC. BIC is identical to the R-function stepAIC with k = log(n). AICc is not available through the R-function stepAIC.
g.region raster=soils_Kfactor -p r.regression.multi mapx=elevation,aspect,slope mapy=soils_Kfactor \ residuals=soils_Kfactor.resid estimates=soils_Kfactor.estim
Available at: r.regression.multi source code (history)
Latest change: Mon Nov 18 20:15:32 2019 in commit: 1a1d107e4f6e1b846f9841c2c6fabf015c5f720d
Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.
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