Upper panel: probability densities of orbital period for single KOIs (gray) and multiple KOIs (outline) for planets with sizes less than 5 R_⊕. These distributions are unlikely to be from the same parent distribution, primarily due to the excess of single-planet systems with orbits near one day. Lower panel: the distribution of planet sizes and orbital periods for single KOI systems. The hot Jupiter and hot super-Earth populations are visible as peaks near 10 R_⊕ and three days and 1 R_⊕ and one day, respectively.