  The ongoing High Accuracy Radial velocity Planet Search (HARPS) has found
that 30-50% of GK dwarfs in the solar neighborhood host planets with
sub-Neptune masses in orbits of P < 50 days. At first glance, this overall
occurrence rate seems inconsistent with the planet frequency measured during
Q0-Q2 of the Kepler Mission, whose 1,235 detected planetary candidates imply
that ~ 15% of main sequence dwarfs harbor short-period planets with R_pl < 4
R_Earth. A rigorous comparison between the two surveys is difficult, however,
as they observe different stellar populations and measure different planetary
properties. Here we report the results of a Monte Carlo study that can account
for this discrepancy via plausible distributions of planetary compositions. We
find that a population concurrently consisting of (1) dense silicate-iron
planets and (2) low-density gas-dominated worlds provides a natural fit to the
current data. In this scenario, the fraction of dense planets decreases with
increasing mass, from f_rocky = 90% at M = 1 M_Earth to f_rocky = 10% at M = 17
M_Earth. Our best fit population has a total occurrence rate of 40% for 2 < P <
50 days and 1 < M < 17 M_Earth, and is characterized by simple power-law
indices of the form N(M)dM ~ M^alpha dM and N(P)dP ~ P^beta dP with alpha =
-1.0 and beta = 0.0. Our model population therefore contains four free
parameters and is readily testable with future observations. Furthermore, our
model's insistence that at least two distinct types of planets must exist in
the survey data indicates that multiple formation mechanisms are at work to
produce the population of planets commonly referred to as "super-Earths".
