b2greek {flexmet}

Find the Greek-Letter Parameterization corresponding to a b Vector of Item Parameters

Description

Convert the b vector of item parameters (polynomial coefficients) to the corresponding Greek-letter parameterization (used to ensure monotonicitiy).

Usage

b2greek(bvec, ncat = 2, eps = 1e-08)

Arguments

bvec

b vector of item parameters (i.e., polynomial coefficients).

ncat

Number of response categories (first ncat - 1 elements of bvec are intercepts)

eps

Convergence tolerance.

Details

See greek2b for more information about the b (polynomial coefficient) and Greek-letter parameterizations of the FMP model.

Value

A vector of item parameters in the Greek-letter parameterization.

References

Liang, L., & Browne, M. W. (2015). A quasi-parametric method for fitting flexible item response functions. Journal of Educational and Behavioral Statistics, 40, 5–34. doi: 10.3102/1076998614556816

See Also

greek2b

Examples

(bvec <- greek2b(xi = 0, omega = 1, alpha = c(.1, .1), tau = c(-2, -2)))
## 0.00000000  2.71828183 -0.54365637  0.29961860 -0.03950623  0.01148330

(b2greek(bvec))
##  0.0  1.0  0.1 -2.0  0.1 -2.0