In a series of articles last week, the writer Megan McArdle asserted that Republicans have about a 75 percent chance of winning the White House in 2016. “Mostly, the White House flips back and forth like a metronome,” she wrote. “Voters just get tired after eight years.”

As other commentators, like Henry Farrell, have pointed out, one can find almost any pattern in presidential results if one looks hard enough. By manipulating the definition of incumbency, the time frame that one examines or the measure of success (e.g., the popular vote or the Electoral College), or by selectively excluding “outliers” or exceptional cases, the potential for cherry-picking and overfitting is high. (In layman’s terms, an overfit statistical model is one that is engineered to match idiosyncratic circumstances in past data, but which is not an accurate picture and makes poor predictions as a result.)

But let’s evaluate a relatively simple version of Ms. McArdle’s claim. What has happened, historically, after the same party has controlled the White House for exactly eight consecutive years? Read more…