You'd think that, but the US has about 724 deaths per 100,000. In a county with fewer than 10,000 people that leaves only about 72 deaths per year. Loving County in Texas has 112 residents. "35 counties have a population under 1,000; 307 counties have a population under 5,000; 709 counties have a population under 10,000" [0].
I haven't read the paper, so I don't know their exact methodology but if they just took a snapshot in 1980 and then in 2014 a county of 10,000 would only be looking at about 145 deaths total. That's small enough that it's pretty possible for outliers to have a big impact. In a county of 1,000 there are only 7 deaths a year, so if you only look at two years that's a total of 14 deaths. It doesn't take a lot to jostle the numbers when you don't have many observations.
In any case, this isn't the main contributor here, as pointed out elsewhere. But it is a good thing to be aware of whenever county level statistics are provided.
It seems they are being smart about using counties:
"All analyses were carried out at the county level. Counties were combined as needed to create stable units of analysis over the period 1980 to 2014, reducing the number of areas analyzed from 3142 to 3110 (eTable 1 in the Supplement). For simplicity, these units are referred to as “counties” throughout."
They also use https://en.wikipedia.org/wiki/Small_area_estimation which seems like a way to deal with the counties with small sizes.
And from what I can tell they are using hierarchical models that should have some regularizing effect from larger populations.
I haven't read the paper, so I don't know their exact methodology but if they just took a snapshot in 1980 and then in 2014 a county of 10,000 would only be looking at about 145 deaths total. That's small enough that it's pretty possible for outliers to have a big impact. In a county of 1,000 there are only 7 deaths a year, so if you only look at two years that's a total of 14 deaths. It doesn't take a lot to jostle the numbers when you don't have many observations.
In any case, this isn't the main contributor here, as pointed out elsewhere. But it is a good thing to be aware of whenever county level statistics are provided.
[0]https://en.wikipedia.org/wiki/County_(United_States)#Populat...