IU is a five seed in the East while the Irish are a six — Purdue is a five in the midwest. Butler's an eight seed, and eight v. nine matchups are a coin toss, odds-wise. The other three slots? Not so much.
ESPN has a pretty smashing article that sums up the percentages on these matchups.
5 vs. 12
The 5-12 matchup is often the first upset pick targeted once brackets are released, and for good reason. From 2008-14, No. 12 seeds actually won 15 of 28 matchups. However, it should be noted that last year was just the fourth time since 1985 that a No. 12 seed failed to win a game (also 1988, 2000 and 2007).
6 vs. 11
While history shows that No. 6 seeds have won 65 percent of meetings with No. 11s, it's truly been a 50/50 proposition in recent years; they have split 24 meetings dating to the 2010 tournament.
Since 2000, only once have the No. 6 seeds won all four meetings with 11 seeds in a single tournament (2004).