Statistical test on a feature that changes over time Let me explain my use case with an example. Let's say some phone manufacturer such as apple iphone monitors hardware failure rates. I have a hypothesis that says the latest ios version is resulting in a higher failure rate. How can I validate this test? Note that the hardware might have run several versions of ios over it's life time. The catch here is that the hardware gets older over time - so we cannot say that the newer ios is causing a higher failure rate. What kind of tests or methodologies can I use to test this hypothesis?

Using time based covariates with survival analysis turned out to be an appropriate method to solve this problem. Here are some useful links.
https://cran.r-project.org/web/packages/survival/vignettes/timedep.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6015946/
