(1)New England's been in 4 of them. Won 3 SU, but covered none. In the '97 Super Bowl I belive they opened at +13.5 to the Packers, but the number closed at 14, so consider that game a betting push. (They lost by 14 pts)
(2) The favorite has won, Straight Up, 17 of the 20. Washington ('88), Denver ('98) and - yep! - the Giants ('91) were the only Dogs to win the game outright.
Biggest dog to pull it off was Denver ('98) +11.5 vs Green Bay.
Which still didn't compare to the classic in '67 (SB III, tho they weren't using fancy Roman numerals then), when Namath and the Jets beat the Balto Colts as a +18 st bernard.
(3)The faves failed to cover 9 of those 20 games (ie, they covered or pushed in 11 of them). The Patriots are the champs when it comes to "failure to cover," at 3. Or at 4,if you count the push.
None of the other multiple contestants in the SB failed to cover as faves even twice, by my count, in the entire history of the SB.
(4) Double Digit favorites in the past two decades are 3-3-1 ATS
And, altho I don't have right at hand the year to year stats that may inidcate a stat-trend, I do know that any team, fave or dog, that is the winner in all three regular season categories will almost always (like 90%) cover in the SB:
Those being: (a) more points scored (again, in the full regular season) than their SB rival; and (b) fewer total points allowed than their SB rival; and (c) fewer total yards allowed than their SB rival.
New England this year is on top for all three categories. This of course has to be tempered by the fact that the Giants played much better the second half of season, and the Pats maybe a little less better (tho they did beat NY in the season finale, but barely).
The above trend works best only if the team so anointed with the stat trifecta is -10 or less.
One final very significant fact: the game is played on a large dirt and grass field (or on a carpet), not on a spread sheet.