ICOMP(IFIM) (Bozdogan, 2003) is calculated as
$$-2LL(theta) + 2C(F^{-1})$$
ICOMP(IFIM-peu) (Koc and Bozdogan, 2015) as
$$-2LL(theta) + k + 2C(F^{-1})$$
ICOMP(IFIM-peuln) (Bozdogan, 2010) as
$$-2LL(theta) + k + 2log(n)C(F^{-1})$$
and CICOMP (Pamukcu et al., 2015) as
$$-2LL(theta) + k(log(n) + 1) + 2C(F^{-1})$$
\(F\) is the fisher information matrix. \(F^{-1}\) is the
reverse Fisher information matrix.
\(C\) is the complexity measure. Four variants are available:
\(C_1\) (Bozdogan, 2010) is
$$C_1(F^{-1}) = s/2*log(lambda_a / lambda_g)$$
\(C_F\) (Bozdogan, 2010) is
$$C_F(F^{-1}) = 1/s*sum_i^s(lambda_i - lambda_a)$$
\(C_1F\) (Bozdogan, 2010) is
$$C_1F(F^{-1}) = 1/(4lambda_a^2)*sum_i^s(lambda_i - lambda_a)$$
\(C_1R\) (Bozdogan, 2000) is
$$C_1R(F^{-1}) = 1/2*log(|R|)$$
Here, \(R\) is the correlation matrix of the model, \(lambda_1, ..., lambda_s\)
are eigenvalues of \(F\), \(lambda_a\) and \(lambda_g\) are arithmetic and
geometric mean of eigenvalues of \(F\), respectively. \(s\) is the dimension
of \(F\).
While calculating the Fisher information matrix (\(F\)), we used
the joint parameters (\(beta,sigma^2\)) of the models. In \(C1R(.)\) function,
we utilized the usual variance-covariance matrix \(Cov(beta)\) of the
models. beta is the vector of regression coefficients.