I have too many environmental variables to use in a multiple regression analysis. If I use all the variables to models are just to complex. The use of the PCA axis in the regression analysis was impossible to interpret (since there wasn't a clear correlation to environmental variables), so we chose to select a limited number of variables, namely the ones that had the higher explanation in PCA... A PCA was used for each set of environmental variables, namely the variables related with the structure of the stream, the evolving vegetation, the climatic, the physical-chemical characteristics of the water from summer period and from winter period, separately. The PCA was performed using the correlation matrix option, using the software PC-ORD, v. 4.21 (McCune & Mefford 1999). For each set of variables, only the variables with coordinates higher to 0.20, for the two first axis, of the CA, were selected to be used in Multiple regression analysis. I could not found literature that confirmes that that's ok to do this, but I think it is not wrong. Can anyone help me?
Best regards, Leena