  We consider the problem of sparse estimation via a lasso-type penalized
likelihood procedure in a factor analysis model. Typically, the model
estimation is done under the assumption that the common factors are orthogonal
(uncorrelated). However, the lasso-type penalization method based on the
orthogonal model can often estimate a completely different model from that with
the true factor structure when the common factors are correlated. In order to
overcome this problem, we propose to incorporate a factor correlation into the
model, and estimate the factor correlation along with parameters included in
the orthogonal model by maximum penalized likelihood procedure. An entire
solution path is computed by the EM algorithm with coordinate descent, which
permits the application to a wide variety of convex and nonconvex penalties.
The proposed method can provide sufficiently sparse solutions, and be applied
to the data where the number of variables is larger than the number of
observations. Monte Carlo simulations are conducted to investigate the
effectiveness of our modeling strategies. The results show that the lasso-type
penalization based on the orthogonal model cannot often approximate the true
factor structure, whereas our approach performs well in various situations. The
usefulness of the proposed procedure is also illustrated through the analysis
of real data.
