Compute bias relative to term-specific true values within grouped simulation results

Computes the mean bias (difference between estimated values and true values) within each group, typically inside evaluate_model_results() for simulation evaluation pipelines.

Usage

eval_bias(x, term = NULL, na.rm = FALSE)

Arguments

x: A numeric vector of estimates (e.g., from a model term).
term: A named numeric vector providing the true value for each term. For example, c("(Intercept)" = 0, x = 2) to specify the true values for each term. If NULL (default), bias is computed relative to zero.
na.rm: Logical; whether to remove missing values when computing the mean bias. Defaults to FALSE.

Value

A numeric scalar representing the mean bias within the current group.

Details

This function is designed to be used inside dplyr::summarise() within a grouped tidyverse pipeline, typically after grouping by term. It computes the mean of x minus the true value for the corresponding term.

If term is provided, the current grouping must include a term variable matching the names in term. If a term in the group is not found in the provided term mapping, the function will return NA with a warning.

Examples

library(dplyr)
library(purrr)
library(broom.mixed)

# Simulate and fit models
sim_models <- tibble(
  id = 1:50,
  model = map(1:50, ~ lm(mpg ~ wt, data = mtcars))
) |>
  extract_model_results()

# Compute bias relative to true value (hypothetical slope = -5)
sim_models |>
  filter(term == "wt") |>
  evaluate_model_results(
    bias = eval_bias(
      estimate,
      term = c("wt" = -5)
    )
  )
#> Error in dplyr::summarise(results, n_models = dplyr::n(), mean_estimate = dplyr::if_else(condition = all(is.na(p.value)),     true = NA_real_, false = mean(estimate, na.rm = TRUE)), mean_std.error = dplyr::if_else(condition = all(is.na(p.value)),     true = NA_real_, false = mean(std.error, na.rm = TRUE)),     power = dplyr::if_else(condition = all(is.na(p.value)), true = NA_real_,         false = mean(p.value < alpha, na.rm = TRUE)), !!!summary_exprs,     !!!{        if (.summarise_standard_broom) {            rlang::exprs(dplyr::across(dplyr::all_of(intersect(broom_cols,                 names(results))), list(mean = mean, sd = sd),                 .names = "{fn}_{col}"))        }        else {            rlang::exprs()        }    }): ℹ In argument: `bias = eval_bias(estimate, term = c(wt = -5))`.
#> Caused by error in `abort()`:
#> ! could not find function "abort"

# Compute bias relative to zero for all terms
sim_models |>
  group_by(term) |>
  evaluate_model_results(
    bias = eval_bias(estimate)
  )
#> # A tibble: 2 × 6
#>   term        n_models mean_estimate mean_std.error power  bias
#>   <chr>          <int>         <dbl>          <dbl> <dbl> <dbl>
#> 1 (Intercept)       50         37.3           1.88      1 37.3 
#> 2 wt                50         -5.34          0.559     1 -5.34