ItemInformationFunc: IIF for 4PLM
Description
Item Information Function for 4PLM
Usage
ItemInformationFunc(a = 1, b, c = 0, d = 1, theta)
Value
Returns a numeric vector representing the item information at each ability
level theta. The information is calculated based on the first derivative of
the log-likelihood of the 4PL model with respect to theta.
Arguments
- a
slope parameter
- b
location parameter
- c
lower asymptote parameter
- d
upper asymptote parameter
- theta
ability parameter