I have a time series sampled in days and when I plot the amplitude vs time it looks like the signal is oscialating at an annual frequency. The series is 15 years long.
Is there a test I can use to test the significance of this frequency in the data? Meaning, test what is the probablity the oscilation is random.
I have used fft and autocorrelation to validate the existence of the period but these tests don't give a probablity measure as far as I know.