  The subject of switchbacks, defined either as large angular deflections or
polarity reversals of the magnetic field, has generated substantial interest in
the space physics community since the launch of Parker Solar Probe (PSP) in
2018. Previous studies have characterized switchbacks in several different
ways, and have been restricted to data available from the first few orbits.
Here, we analyze the frequency of occurrence of switchbacks per unit distance
for the first full eight orbits of PSP. In this work, are considered switchback
only the events that reverse the sign of magnetic field relative to a regional
average. A significant finding is that the rate of occurrence falls off sharply
approaching the sun near 0.2 au (40 $R_\odot$), and rises gently from 0.2 au
outward. The analysis is varied for different magnetic field cadences and for
different local averages of the ambient field, confirming the robustness of the
results. We discuss implications for the mechanisms of switchback generation. A
publicly available database has been created with the identified reversals.
