If you care about the validity of the study then you should care about what the context of the data. That is why you would care about the history of those counties, if you care about the conclusions of the study. Its just one of many gaping holes in the study. And if you are going to bring up the conclusion that places experiencing the opioid crisis were more likely to vote for Trump then you should have data to support that. Again, the crisis didn't begin and end in 2015. There were several elections during this crisis. Thats if you care about the validity of the study, though.
Trump and Hillary and Obama and Sanders and Stein all spoke about the opioid crisis. None of them conducted a study to make a correlation between the opioid epidemic and voting for Trump. The agenda is pretty clear. Its made all the more clear when such a shoddy study is published.
My criticisms are absolutely valid.
There were no studies about any of the others because none of the others won. You posted a link about the growth of the opioid crisis during Obama's time in office. Mitt Romney and John McCain were both still alive at time, no one wrote a piece on what they did/didn't do to address the problem....because they didn't win the election so it doesn't matter. It's a 2 decade old problem. You want studies related to everyone as if their relevance is on the same level as that of the POTUS?
That's what your criticism lacks validity. Your primary complaint seems to be that the study combines an unpleasant scenario and a mention of their voting patterns. You allege "context" but the opioid crisis wasn't a political issue in 2000, 2004, 2008, 2012. It was a political issue in 2016 and so the voting patterns are being paid attention to in 2016.
The other failure of your criticism is that you're not criticizing the study for what it says, your criticism is that other people didn't do similar studies for other elections also. But there was only 1 Presidential election after this crisis became a mainstream issue - the 2016 election. However, there are plenty of stories about what was being done prior to the 2016 election and how elected officials, including the POTUS of the time, Obama, weren't doing enough.
You don't have any consistency here. Do you have a problem with stories blaming Obama's treatment of the issue from pre-2016? Were those stories about an "agenda"? Do you have a problem with this being a political issue going back several years? Or do you only have a problem with this specific study?
To summarize, the opioid crisis became a mainstream political issue during Obama's term in office. Stories were written about this growing section of the population. The population group was being studied and analyzed from multiple angles. All of this fine...until they also study the voting patterns of these people. And then, only then, does it become an "agenda".
I'm sorry but that is not a valid critique of anything if you're going to ignore the years of political attention to this issue to only find a fault with it in 2018.