Category-score moments for a polytomous item

Category-score moments for a polytomous item

Usage

item_moments(theta, tau_i, disc = 1)

Arguments

theta

Person location, in logits.

tau_i

Numeric vector of the item's threshold parameters.

disc

Discrimination (frame unit) multiplier on the exponent; 1 for the ordinary Rasch model.

Value

A list with category probabilities P, expected score E, variance V, and third and fourth central moments mu3, mu4.

Examples

item_moments(0.5, c(-1, 0, 1))
#> $P
#> [1] 0.0576288 0.2582744 0.4258225 0.2582744
#> 
#> $E
#> [1] 1.884742
#> 
#> $V
#> [1] 0.7337796
#> 
#> $mu3
#> [1] -0.2057782
#> 
#> $mu4
#> [1] 1.285077
#>