Why is this different from outcomes predicted by other modelers, such as Alan Abramowitz and John Sides/Eric McGhee? Part of it is that the predicted outcomes really aren’t that different. Abramowitz’s most likely outcome is a GOP pickup of six, while this model’s most likely outcome is a pickup of eight. This has great substantive importance, but in statistical terms, the findings are well within the confidence intervals of the various models.

These other models also take a much broader swath, putting results from back to the 1950s into their data set. One of the assumptions behind this model is that something has substantially changed in the past few cycles as we’ve become increasingly polarized. Red states don’t vote for blue senators except in exceptional circumstances, and vice versa. There’s some support for this in the Sides/McGhee models; if they base their predictions off of findings from 1980 to the present, instead of from 1952 to the present, they find that Tom Cotton’s chances of winning in Arkansas skyrocket.

At the end of the day, it’s important to remember that these models are largely heuristic devices, especially this far out. There’s also still a lot we don’t know: While the model predicts 2006 quite well when you know who the “problem” senators will be and that Bush’s job approval will be at 39 percent on Election Day, it suggests that Republicans are likely to lose only three Senate seats when you randomize his job approval and don’t yet know that Burns or Allen will be badly damaged incumbents on Election Day.