It’s an oversimplification in the media, this is a time series analysis esp. at the macro level. Then you do some fancy math and estimate the counter factual ->

It’s an oversimplification in the media, this is a time series analysis esp. at the macro level. Then you do some fancy math and estimate the counter factual -> the delta between observed and estimated is your excess mortality. Google has a tool for doing this called CausalImpact (available as an R & Python library if you want to play with a tool that can do this analysis).