Donna C wrote:

It is easier to find giant planets with close-in orbits. They induce the
largest changes and in the shortest time frame to the Doppler velocities that
are measured. Planets with smaller masses induce less changes in the
star's velocity. The further out the planet orbits, the velocity changes
are smaller and it takes more time to see the effect. So the data is
going to biased to giant planets with close orbits.

Note, however, that these observations were made with interferometry,
not astrometric methods of the kind that have been used to detect
most of the extrasolar planets discovered so far. Each technique will
have its own biases, but I think we can expect a better picture of
the types of planetary system, and their relative abundance, as more
methods are brought to bear.

--Odysseus