Several classes of pulsating stars are now known to undergo slow changes in amplitude; these include pulsating red giants and supergiants, and yellow supergiants. We have used visual observations from the AAVSO International Database and wavelet analysis of 39 red giants, 7 red supergiants, and 3 yellow supergiants to test the hypothesis that an increase in amplitude would result in an increase in period because of non-linear effects in the pulsation. For most of the stars, the results are complex and/or indeterminate, due to the limitations of the data, the small amplitude or amplitude variation, and/or other processes such as random cycle-to-cycle period fluctuations. For the carbon giants, however, of those which have substantial amplitude variation, and reasonably simple behavior, over 90 % show a positive correlation between amplitude and period. For the non-carbon giants, and the red and yellow supergiants, the numbers showing positive and negative correlation between amplitude and period are comparable.
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