MAKING HABITS, BREAKING HABITS: Why We Do Things, Why We Don't, and How to Make Any Change Stick, by Jeremy Dean. Da Capo Lifelong, 264 pp., $26.

You've probably read that it takes only 21 days to create a new habit. But science hasn't substantiated that figure, writes Jeremy Dean, creator of PsyBlog, a website analyzing psychological studies. New research says that cementing a simple habit, like drinking a glass of water after breakfast, might take 21 days, but a more complicated one could take nearly a year.

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THE SCOOP You know that Hershey's bar at 3 p.m.? It's a temptation, not a habit, Dean writes. Don't try to repress the thought -- if someone says not to think of a white bear, what pops up into your head?

THE BOTTOM LINE Don't go for complete reinvention, he writes. Instead, make a specific plan called an implementation intention, and be positive: If I'm hungry between meals, then I will eat an apple -- not if I'm hungry between meals, then I must avoid chocolate.