Time study of subsidence

hi all
I did all the steps for the deformation measurement including COREGISTRATION to TERRAIN CORRECTION and after that PHASE TO HEIGHT CONVERSION. my question is, how can I compare the result of data 2016,2017 and 2018 or time study of subsidence in any particular area?
Or I have to process data set of 2016,2017 and 2018?
thanks in advance