Dear all,

I am trying to fit a multiple linear regression model to a table of data. My
data.frame is like this ...

fit.data <- data.frame(y, x1, x2, x3, x4, x5, x6), then I use the linea
regression command ...

lm(formula = y ~ x1 + x2 + x3 + x4 + x5 + x6, data = fit.data)

however, for some tables the data in column x1 is equal to -x2, so I get NA
values for both coefficients of x1 and x2. I need to have real fitted
coefficients for all the parameters or the physical meaning of the
parameters is lost. Is there any way of forcing R to fit all the parameters?
I have seen the contrast option but I don't really understand it (I am not a
statistician) so I would be greatful if anyone could explain that.

Kind Regards

Chibisi

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