  We analyze magnetic field data from the first six encounters of PSP, three
Helios fast streams and two Ulysses south polar passes covering heliocentric
distances $0.1\lesssim R\lesssim 3$ au. We use this data set to statistically
determine the evolution of switchbacks of different periods and amplitudes with
distance from the Sun. We compare the radial evolution of magnetic field
variances with that of the mean square amplitudes of switchbacks, and quantify
the radial evolution of the cumulative counts of switchbacks per km. We find
that the amplitudes of switchbacks decrease faster than the overall turbulent
fluctuations, in a way consistent with the radial decrease of the mean magnetic
field. This could be the result of a saturation of amplitudes and may be a
signature of decay processes of large amplitude Alfv\'enic fluctuations in the
solar wind. We find that the evolution of switchback occurrence in the solar
wind is scale-dependent: the fraction of longer duration switchbacks increases
with radial distance whereas it decreases for shorter switchbacks. This implies
that switchback dynamics is a complex process involving both decay and in-situ
generation in the inner heliosphere. We confirm that switchbacks can be
generated by the expansion although other type of switchbacks generated closer
to the sun cannot be ruled out.
