# Multifractional polynomial with mixed-effects logistic model

## Dataset

Unfortunately, I posted this question on cross-validated and have yet to get an answer (see here).
I am working on a dataset collected from more than 20 hospitals. I used the `glmer` command to estimate a mixed-effects logistic regression model with the following as patient-level predictors:

• age (patient’s age; a continuous variable),
• cci (Charlson Comorbidity Index; a continuous variable),
• sex (patient’s sex; man vs. woman),
• race (patient’s race; Asian vs. Black vs. South Asian vs. White), and
• htn (has hypertension vs. no hypertension).

I used the hospital variable (the hospital that recruited patients) to estimate the random intercept.

## Problem

My code for mixed-model (worked very smoothly):
`mixed_died30in <- glmer(died30in ~ age + cci + sex + race + htn + infx_source + (1 | hospital), data = passem, family = binomial, control = glmerControl(optimizer = "Nelder_Mead"), nAGQ = 10)`

Then I used the `mfp` command:
`mfp_died30in <- mfp(glmer(died30in ~ fp(age, df = 4, select = 0.05) + fp(cci, df = 4, select = 0.05) + sex + race + htn + infx_source + (1 | hospital), family = binomial, data = passem, control = glmerControl(optimizer = "Nelder_Mead"), nAGQ = 10))`

The following error appeared:

``````Error in fixed.only && random.only : invalid 'x' type in 'x && y'
In addition: Warning message:
In checkConv(attr(opt, "derivs"), opt\$par, ctrl = control\$checkConv,  :
Model is nearly unidentifiable: large eigenvalue ratio
- Rescale variables?
``````

## Questions

• Does the `mfp` command from the mfp package in R support mixed-effect models?
• Is (are) there any problem(s) in my code?

Any help would be so appreciated
Abdullah

I doubt that a method that does stepwise variable selection will work in many contexts. But you need to put this question to the maintainer of that function.

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Thank you so much Professor, I will contact the maintainer

I will reply on Cross-validated with a couple of ideas.

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