The X axis expresses "how Republican is the precinct" as inferred by the percentage of precinct voters that chose the Straight Republican option.
The Y axis shows if the Individual Candidate voters were "more or less favorable to Trump". They do this by plotting the difference between these voters' Trump % to the the straight Republican voters' split.
For example, in a precinct which had 80% Straight Republican (vs 20% Straight Democrat) but only 20% Individual Trump (vs 80% Individual Biden), you'd put that precinct as a -60% on the Y axis.
They do this by plotting the difference between these voters' Trump % to the the straight Republican voters' split.
This is the problem right here. He is creating a function with y dependent on x, and then acting surprised that there is a relationship between y and x.
The function for Y is chosen to make the visualization clear. You could also express it as the split between Trump and Biden for Individual Choice voters, and you’d see a trend after 20ish% of X where Y skews towards Biden linearly.
The X axis expresses "how Republican is the precinct" as inferred by the percentage of precinct voters that chose the Straight Republican option.
The Y axis shows if the Individual Candidate voters were "more or less favorable to Trump". They do this by plotting the difference between these voters' Trump % to the the straight Republican voters' split.
For example, in a precinct which had 80% Straight Republican (vs 20% Straight Democrat) but only 20% Individual Trump (vs 80% Individual Biden), you'd put that precinct as a -60% on the Y axis.
This is the problem right here. He is creating a function with y dependent on x, and then acting surprised that there is a relationship between y and x.
The function for Y is chosen to make the visualization clear. You could also express it as the split between Trump and Biden for Individual Choice voters, and you’d see a trend after 20ish% of X where Y skews towards Biden linearly.