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

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



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.


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


A string that selects a subset in the itembank that makes up the key, the set of difficulty estimates from a fitted Rasch model. The built-in keys are: "gsed2212" (default), "gsed2208" (deprecated), "gsed2206" (deprecated), "gsed1912", "lf2206", "sf2206", "gcdg", and "dutch". Since version 1.5.0, the key = "gsed" selects the latest key starting with the string "gsed". Use key = "" to use all item names, which should only be done if there are no duplicate itemnames in the itembank.


A data.frame with columns key, item, tau, instrument, domain, mode, number and label. Only columns item and tau are required. The function uses dscore::builtin_itembank by default.


A string describing the population. Currently supported are "phase1" (default), "dutch", "gcdg".


A string specifying the unit in which age is measured (either "decimal", "days" or "months"). The default ("decimal") means decimal age in years.


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


The function internally defines a scale factor given the key.


get_age_equivalent(c("gpagmc018", "gtogmd026", "ddicmm050"))
#> # A tibble: 9 × 4
#>   item          d   pct       a
#>   <chr>     <dbl> <dbl>   <dbl>
#> 1 gpagmc018  14.5    10  0.0610
#> 2 gpagmc018  23.4    50  0.295 
#> 3 gpagmc018  32.3    90  0.501 
#> 4 gtogmd026  31.1    10  0.473 
#> 5 gtogmd026  40      50  0.708 
#> 6 gtogmd026  48.9    90  1.04  
#> 7 ddicmm050  68.7    10  2.44  
#> 8 ddicmm050  77.7    50  4.25  
#> 9 ddicmm050  86.6    90 NA