irtoys: tif – R documentation

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tif

Test information function

Description

Returns the test information function (TIF) of the 3PL (1PL, 2PL) model. The TIF is the sum of the item information functions (IIF) in a test, and indicates the precision of measurement that can be achieved with the test at any value of the latent variable, bein inversely related to measurement variance.

Usage

tif(ip, x = NULL)

Arguments

`ip`	Item parameters: the output of est.
`x`	The values of the latent variable (θ in the equation above), at which the TIF will be evaluated. If not given, 99 values spaced evenly between -4 and +4 will be used, handy for plotting.

Details

A common use of this function would be to obtain a plot of the TIF.

Value

A list of:

`x`	A copy of the argument `x`
`f`	A vector containing the TIF values

Author(s)

Ivailo Partchev

Examples

plot(trf(Scored2pl))

irtoys

A Collection of Functions Related to Item Response Theory (IRT)

v0.2.1

GPL (>= 2)

Authors

Ivailo Partchev [aut, cre], Gunter Maris [aut], Tamaki Hattori [ctb]

Initial release

2017-12-15

tif