| 摘要 | Since declaring his candidacy for the Democratic presidential nomination, former vice president Joe Biden has shot up in the polls. He now is at 38.3% nationally in the RealClearPolitics polling average, up from 29% a month ago, and holds a 19.5 percentage point lead over his nearest competitor. He has surged to a 13-point lead in New Hampshire (his lead in Iowa is smaller, but Iowa has not been polled recently).
What does this mean? Analysts were openly skeptical of Biden’s chances as the Democratic nominee, and he seemed beset by early polling surges from Bernie Sanders, Pete Buttigieg, and Kamala Harris. There were structural reasons to doubt whether his candidacy was viable as well.
Should analysts change their thinking on Biden now? That would probably be premature. Rather, analysts should proceed as Bayesians. What does this mean? The Bayesian approach to statistics acknowledges that new information is not evaluated on a blank slate. While it admits that we should adjust our views in light of new data, it also reminds us that we should not forget about everything we knew (or thought we knew) beforehand either.
This isn’t an approach you probably learned in your Statistics 101 class, but the suggestion is not that we apply Bayes’ Rule in a mathematical sense (which can be difficult outside of the circumstances where an analyst has clearly defined prior beliefs). Instead, it is that analysts should simply avoid the temptation to react to each new piece of information in a vacuum. We should move from our prior beliefs slowly, unless we receive overwhelming evidence to the contrary.
So where does this leave us with respect to Biden? His poll surge is impressive, and it probably reflects an improved chance of winning the Democratic nomination. He’s handled his rollout well, and seems to understand that there is a wide lane of moderate and conservative Democrats that has been left largely untouched by the major Democratic candidates. So, he’s probably somewhat more likely to be the nominee than before.
At the same time, this campaign is a marathon, not a sprint, and with over 20 serious Democratic candidates running, it is likely to have multiple twists before the election season is over. Moreover, all of Biden’s previous issues remain: He’s still a white male septuagenarian with #MeToo issues in a party that increasingly defines itself as young, female, and diverse. And he’s still never won a presidential primary.
Perhaps more importantly, while Biden is a household name for political junkies, most Americans know relatively little about him other than that he was Barack Obama’s vice president – if that. It’s not entirely surprising that he received a bump after his announcement, given the attention that his rollout received. There’s a reasonable chance he will follow the pattern of “discovery, scrutiny, and decline” that political scientists John Sides and Lynn Vavreck coined to describe the 2012 Republican field. This describes a pattern where candidates receive media coverage, leading to a surge in the polls, only to see that surge recede as scrutiny sets in.
Yes, he could end up being the Democratic nominee, and if he’s still in his current position after the first few Democratic debates, we should take a more serious look at the prospect that he might put an end to the Democratic primary fight early. But for now, not much has really changed. |
