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As someone who conducts large scale studies, longitudinal studies rarely have a control group (particularly when the topic you are examining has multiple confluencing variables). The latter is of particular importance - you are looking at healthcare outcomes over two decades. The number of variables (both known and unknown) that can impact the results are in the thousands. The goal of the study is inferential analysis, not causal analysis (the latter being impossible due to the lack of controls).Don’t answer questions just inject the aluminum into babies
Once again, most time series studies do not have a control group (in the conventional sense).