```
model <- lm(Sepal.Length ~ Petal.Length * Species, data = iris)
dof(model)
model <- glm(vs ~ mpg * cyl, data = mtcars, family = "binomial")
dof(model)
if (FALSE) {
if (require("lme4", quietly = TRUE)) {
model <- lmer(Sepal.Length ~ Petal.Length + (1 | Species), data = iris)
dof(model)
}
if (require("rstanarm", quietly = TRUE)) {
model <- stan_glm(
Sepal.Length ~ Petal.Length * Species,
data = iris,
chains = 2,
refresh = 0
)
dof(model)
}
}
```

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