get_age_equivalent function

Get age equivalents of items that have a difficulty estimate

This function calculates the ages at which a certain percent in the reference population passes the items.

get_age_equivalent(
  items,
  pct = c(10, 50, 90),
  key = NULL,
  population = NULL,
  transform = NULL,
  itembank = dscore::builtin_itembank,
  xunit = c("decimal", "days", "months"),
  verbose = FALSE
)

Arguments

• items: A character vector containing names of items to be included into the D-score calculation. Milestone scores are coded numerically as 1 (pass) and 0 (fail). By default, D-score calculation is done on all items found in the data that have a difficulty parameter under the specified key.

• pct: Numeric vector with requested percentiles (0-100). The default is pct = c(10, 50, 90).

• key: String. Name of the key that bundles the difficulty estimates pertaining one the same Rasch model. View builtin_keys for an overview of the available keys.

• population: String. The name of the reference population to calculate DAZ. Use unique(builtin_references$population) to obtain the set of currently available reference populations.

• transform: Numeric vector, length 2, containing the intercept and slope of the linear transform from the logit scale into the the D-score scale. The default (NULL) searches builtin_keys

  for intercept and slope values.

• itembank: A data.frame with at least two columns named item and tau. By default, the function uses dscore::builtin_itembank. If you specify your own itembank, then you should also provide the relevant transform and qp arguments.

• xunit: A string specifying the unit in which age is measured (either "decimal", "days" or "months"). The default "decimal" corresponds to decimal age in years.

• verbose: Logical. Print settings.

Returns

data.frame with four columns: item, d (D-score), pct (percentile), and a (age-equivalent, in xunit units).

Note

The function internally defines a scale factor given the key.

Examples

get_age_equivalent(c("gpagmc018", "gtogmd026", "ddicmm050"))