  Latent variable models are well-known to suffer from rank deficiencies,
causing problems with convergence and stability. Such problems are compounded
in the "reduced-group split-ballot multitrait-multimethod model", which omits a
set of moments from the estimation through a planned missing data design. This
paper demonstrates the existence of rank deficiencies in this model and give
the explicit null space. It also demonstrates that sample size and distance
from the rank-deficient point interact in their effects on convergence, causing
convergence to improve or worsen depending on both factors simultaneously.
Furthermore, it notes that the latent variable correlations in the uncorrelated
methods SB-MTMM model remain unaffected by the rank deficiency. I conclude that
methodological experiments should be careful to manipulate both distance to
known rank-deficiencies and sample size, and report all results, not only the
apparently converged ones. Practitioners may consider that, even in the
presence of nonconvergence or so-called "inadmissible" estimates, a subset of
parameter estimates may still be consistent and stable.
