This function performs konfound analysis on a linear mixed-effects model object produced by lme4::lmer. It calculates the sensitivity of inferences for fixed effects in the model. It supports analysis for a single variable or multiple variables.

## Usage

```
konfound_lmer(
model_object,
tested_variable_string,
test_all,
alpha,
tails,
index,
to_return
)
```

## Arguments

- model_object
The mixed-effects model object produced by lme4::lmer.

- tested_variable_string
The name of the fixed effect being tested.

- test_all
Boolean indicating whether to test all fixed effects or not.

- alpha
Significance level for hypothesis testing.

- tails
Number of tails for the test (1 or 2).

- index
Type of sensitivity analysis ('RIR' by default).

- to_return
The type of output to return.