The three sort of x-factors in going from polling to the final result in Iowa are:
1) Ground game
2) Second choices / realignment
3) Votes to delegates ratio (helps candidates with rural support)
1) Ground game
2) Second choices / realignment
3) Votes to delegates ratio (helps candidates with rural support)
Generally speaking I'd expect Buttigieg, Warren and Sanders to get help from No. 1.
No. 2 is maybe the hardest to say—and probably the most important—but generally Warren and Buttigieg are helped most by 2nd choice support.
No. 3 likely helps Buttigieg, Klobuchar and Biden.
No. 2 is maybe the hardest to say—and probably the most important—but generally Warren and Buttigieg are helped most by 2nd choice support.
No. 3 likely helps Buttigieg, Klobuchar and Biden.
Overall, then, I have the 3rd and 4th place candidates (Buttigieg/Warren) being helped more than 1 and 2 (Bernie/Biden) by these factors. So that's a reason to still treat Iowa as a 4-way (at least) race.
Even if you treat these factors as "known unknowns" and think it's silly to guess at who might benefit from them (not unreasonable, especially for 2nd choices) they still contribute a lot to uncertainty—and remember that final Iowa results are often pretty far from final polls.
