Chronic exposure as a function of covariates¶
The intake frequency and transformed intake amounts may be modelled as a function of covariates. MCRA allows one covariable and/or one cofactor.
Frequencies |
Amounts |
|
---|---|---|
cofactor |
logit(π)=β0l |
transf(yij)=β0l+ci+uij |
covariable |
logit(π)=β0+β1f(x1;df) |
transf(yij)=β0+βlf(x1;df)+ci+uij |
both |
logit(π)=β0l+β1f(x1;df) |
transf(yij)=β0l+βlf(x1;df)+ci+uij |
interaction |
logit(π)=β0l+β1lf(x1;df) |
transf(yij)=β0l+β1lf(x1;df)+ci+uij |
Here l=1⋯L and L is the number of levels of the cofactor, yij , the intake amount, x1 is the covariable, f is a polynomial function with the degrees of freedom df, ci and uij are the individual effect and interaction effect, respectively. These effects are assumed to be normally distributed N(0,σ2between) resp. N(0,σ2within). The degree of the function is determined by backward or forward selection. In the output, the usual intake is displayed for a specified number of values of the covariable and/or the levels of the cofactor.