I am using an accelerometer to test for vibration. To clarify the physics, imagine an accelerometer (which measures acceleration) is sitting on top of a washing machine. On the spin cycle the accelerometer will move up and down, giving a continuous(ly changing sample) reading with the mean being earth's gravity. Put one wet towel in the machine, and the accelerometer will move up and down more, with (aprox) the same frequency. How can I tell if there is a wet towel?
As long as my samples are larger than the period (and the period of any harmonics I guess) then the mean is going to be constant. I want to test for change (quickly, and preferably formally) . The undergraduate text book I have doesn't seem to help; I was hoping to use the apache commons stats package: https://commons.apache.org/proper/commons-math/userguide/stat.html
I guess, given the above, I can take the mean of just the positive values from both samples and perform a one tailed test, but the distribution of the positive values will be awfully skewed...
The discussion here: Compare the variances of several groups Does seem to be the answer (note the comments below on ANOVA).
I am surprised my problem is not more mainstream - variance of variance, I would have thought, would have many uses. Mean number of people in hospital dying of the flu/covid-19 for instance is quite constant across the country I believe, but the rate in individual hospitals presumably varies enormously as the disease spreads. P