For 20 consecutive years, from 1980-99, America’s favorite race crushed the favorite. Not one won the Kentucky Derby in the Eighties or Nineties. Yet the last four post-time betting choices — Orb, California Chrome, American Pharoah and Nyquist — finished first.

Coincidence? Probably not. Many think the reason was switching the qualifying criteria from graded-stakes earnings, which included 2-year-old sprints, to a points system emphasizing 3-year-old stakes. The change in 2013 helped weed out sprint types who set unrealistically fast paces that cooked contenders.

Graham Motion, who trained 2011 Derby winner Animal Kingdom, won’t dispute that theory.

“It’s certainly possible,” he said. “There’s nothing else that’s changed about the Derby, so it certainly makes sense. But [four straight winning favorites] is pretty remarkable, because it’s such a difficult race to win.”

And to predict. Handicappers agonize for months looking for “my Derby horse,” and few springs have been as confusing as this one.

Dale Romans trains longshot J Boys Echo. “I think it’s as wide open as we’ve seen in a long time,” he said. “I think you’re going to have big odds on whoever the favorite ends up being. I don’t think this really means it’s a bad group of horses. I think it’s an even group of horses.”

Last year, Nyquist came to Churchill Downs undefeated. Either you figured he was the one to beat or you tried to beat him. Six days from Derby 143, even the identity of the favorite is uncertain. Best guess is reigning 2-year-old champion Classic Empire, who at his best looks like a standout. Yet he has flaws that will make players think twice. He’s a temperamental sort who refused to work out twice this year, when a foot abscess and back trouble interrupted his preparation.

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A gritty, off-the-pace victory in the Arkansas Derby returned Classic Empire to the top of many Derby lists. That was his first race since Feb. 4, and he’s coming back in only three weeks, which he’s never done. Red flag.

“It’s been a tough road,” trainer Mark Casse said. “But luckily, the last month has gone very well. Do I wish we had another start? Of course I do. But he has a tremendous amount of ability, and I feel he’s the most talented horse out there right now.’’

Florida Derby winner Always Dreaming and Motion’s Irish War Cry, who dominated the Wood Memorial, also are serious contenders. Casse calls them “the horses I would probably fear the most.”

It would shock no one if none of those three won, and every horse in the field has holes in his form. Points leader Girvin is 3-for-4 but has raced only at the Fair Grounds, where his competition was suspect, and he’s battling a cracked hoof. McCraken must rebound from a so-so third in the Blue Grass, his only loss in five starts, after a two-month absence with an ankle strain. Deep closer Gunnevera needs a fast pace and a trouble-free trip, and he may get neither.

Todd Pletcher’s best chance is Always Dreaming, the perfect name for a Derby colt. His Florida Derby runaway, his stakes debut, instantly raised his stature. Yet Pletcher, 1-for-45 in the Derby, had many runners with this profile who were nowhere in Louisville.

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“Well, it’s definitely been an interesting winter and spring,” Pletcher said, “and the horses have been back and forth. Some of them look impressive and then not impressive and then come back and run well.”

So who will peak and who will regress Saturday? The right answer will inflate your ego and fatten your wallet. Figure it out.