Searches the item bank for matching items, and returns the difficulty estimates. Matching is done by item name. Comparisons are done in lower case.

get_tau(items, key = "gsed", itembank = dscore::builtin_itembank)

## 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. A string that sets the key, the set of difficulty estimates from a fitted Rasch model. The built-in keys are: "gsed" (default), "gcdg", and "dutch". Use key = "" to use all item names, which should only be done if there are no duplicate itemnames. 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.

## Value

A named vector with the difficulty estimate per item with length(items) elements.

builtin_itembank(), dscore()
# difficulty levels in the GHAP lexicon
#>      5.51        NA        NA