tif function

Test information function

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.

tif(ip, x = NULL)

Arguments

• ip: Item parameters: the output of $est$.
• x: The values of the latent variable ($\theta$ 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.

Returns

A list of: - x: A copy of the argument x - f: A vector containing the TIF values

Details

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

Examples

plot(trf(Scored2pl))

See Also

plot.tif, iif

Author(s)

Ivailo Partchev