  In order to extend our previous studies of the unexplained phenomenon of
cyclic amplitude variations in pulsating red giants, we have used the AAVSO
time-series analysis package VSTAR to analyze long-term AAVSO visual
observations of 50 such stars, mostly Mira stars. The relative amount of the
variation, typically a factor of 1.5, and the time scale of the variation,
typically 20-35 pulsation periods, are not significantly different in
longer-period, shorter-period, and carbon stars in our sample, and they also
occur in stars whose period is changing secularly, perhaps due to a thermal
pulse. The time scale of the variations is similar to that in smaller-amplitude
SR variables, but the relative amount of the variation appears to be larger in
smaller-amplitude stars, and is therefore more conspicuous. The cause of the
amplitude variations remains unknown.
