Plot Effective Size by Confidence Level

Creates a ggplot visualization showing how effective lineup size varies across confidence levels.

Usage

plot_effective_size_conf(
  ppv_range_obj,
  show_nominal = TRUE,
  show_points = TRUE
)

Arguments

ppv_range_obj

A lineup_ppv_range object from ppv_range_by_confidence(), or a dataframe with columns: confidence, effective_size

show_nominal

Logical. Whether to show nominal lineup size as reference line (default = TRUE)

show_points

Logical. Whether to show points at each confidence level (default = TRUE)

Value

A ggplot2 object

Details

Effective size < nominal size indicates lineup bias, where some members are implausible and rarely chosen. This can vary by confidence level if witnesses at different confidence levels have different lineup viewing strategies.

A horizontal line at the nominal lineup size provides a reference. Values below this line indicate bias; values at or above indicate fair lineups.

Examples

data(lineup_example)
ppv_range <- ppv_range_by_confidence(lineup_example,
                                     confidence_bins = c(0, 60, 80, 100))
#> Target-absent lineups contain a designated innocent suspect, so innocent-suspect IDs are counted directly and no lineup-size correction is applied. The nominal, effective and uncorrected estimates are therefore identical for these data. The three diverge only when no innocent suspect is designated and the number of innocent-suspect IDs has to be estimated from the filler IDs.
plot_effective_size_conf(ppv_range)
#> Warning: Removed 3 rows containing missing values or values outside the scale range
#> (`geom_line()`).
#> Warning: Removed 3 rows containing missing values or values outside the scale range
#> (`geom_point()`).