# fix.coef: Fix coefficients and update model In mice: Multivariate Imputation by Chained Equations

 fix.coef R Documentation

## Fix coefficients and update model

### Description

Refits a model with a specified set of coefficients.

### Usage

``````fix.coef(model, beta = NULL)
``````

### Arguments

 `model` An R model, e.g., produced by `lm` or `glm` `beta` A numeric vector with `length(coef)` model coefficients. If the vector is not named, the coefficients should be given in the same order as in `coef(model)`. If the vector is named, the procedure attempts to match on names.

### Details

The function calculates the linear predictor using the new coefficients, and reformulates the model using the `offset` argument. The linear predictor is called `offset`, and its coefficient will be `1` by definition. The new model only fits the intercept, which should be `0` if we set `beta = coef(model)`.

### Value

An updated R model object

### Author(s)

Stef van Buuren, 2018

### Examples

``````model0 <- lm(Volume ~ Girth + Height, data = trees)
formula(model0)
coef(model0)
deviance(model0)

# refit same model
model1 <- fix.coef(model0)
formula(model1)
coef(model1)
deviance(model1)

# change the beta's
model2 <- fix.coef(model0, beta = c(-50, 5, 1))
coef(model2)
deviance(model2)

# compare predictions
plot(predict(model0), predict(model1))
abline(0, 1)
plot(predict(model0), predict(model2))
abline(0, 1)

# compare proportion explained variance
cor(predict(model0), predict(model0) + residuals(model0))^2
cor(predict(model1), predict(model1) + residuals(model1))^2
cor(predict(model2), predict(model2) + residuals(model2))^2

# extract offset from constrained model
summary(model2\$offset)

# it also works with factors and missing data
model0 <- lm(bmi ~ age + hyp + chl, data = nhanes2)
model1 <- fix.coef(model0)
model2 <- fix.coef(model0, beta = c(15, -8, -8, 2, 0.2))
``````

mice documentation built on June 7, 2023, 5:38 p.m.