  The Kepler space mission has detected a large number of exoplanets in
multiple transiting planet systems. Previous studies found that these Kepler
multiple planet systems exhibit an intra-system uniformity, namely planets in
the same system have similar sizes and correlated orbital spacings. However, it
is important to consider the possible role of selection effects due to
observational biases. In this paper, we revisit the orbital spacing aspect of
the pattern after taking observational biases into account using a forward
modeling method. We find that orbital spacings, in terms of period ratios, of
Kepler multiple planet systems are significantly correlated only for those
tightly packed systems, and the transition from correlation to non-correlation
is abrupt with a boundary at mean period ratio $\overline{PR}$ $\sim 1.5 -
1.7$. In this regard, the pattern of orbital spacing is more like a dichotomy
rather than a global correlation. Furthermore, we find that such an apparent
orbital spacing dichotomy could be essentially a projection of a dichotomy that
related to mean motion resonance (MMR), which we dub as MMR dichotomy, and
itself could be a natural result of planet migration and dynamical evolution.
