Problem with your analysis is that in Shivs’s analysis the graph is constant for a while and then starts dropping, so your analysis wouldn’t be accurate either.
This is just a model to illustrate why a negative slope is expected.
Trump won a certain pct of Dems and a certain pct of Repubs. When the overall Dem pct is high, he's going to outperform Repubs. When the overall Repub vote is high, he's going to underperform Repubs. This is just a mathematical certainty.
A negative slope is expected with random values, the point is the correlation between Republican straight party vote and Trump single vote is not random, you would expect it to be a fairly constant ratio, aka a straight line.
Problem with your analysis is that in Shivs’s analysis the graph is constant for a while and then starts dropping, so your analysis wouldn’t be accurate either.
This is just a model to illustrate why a negative slope is expected.
Trump won a certain pct of Dems and a certain pct of Repubs. When the overall Dem pct is high, he's going to outperform Repubs. When the overall Repub vote is high, he's going to underperform Repubs. This is just a mathematical certainty.
A negative slope is expected with random values, the point is the correlation between Republican straight party vote and Trump single vote is not random, you would expect it to be a fairly constant ratio, aka a straight line.