Ninety percent of Americans say they pray - for their health, or their love life or their final exams. But does prayer do any good? For decades, scientists have tried to test the power of prayer and positive thinking, with mixed results. Now some scientists are fording new - and controversial - territory. When I first meet Sheri Kaplan, she is perched on a plastic chair at a Miami clinic, holding out her arm as a researcher draws several vials of blood. I'm quite excited about my blood work this time," she says. "I've got no stress and I'm proud of it." Kaplan is tanned and freckled, with wavy red hair and a cocky laugh. She is defiantly healthy for a person who has lived with HIV for the past 15 years. "God didn't want me to die or even get sick," she asserts. "I've never had any opportunistic infections, because I had no time to be down." Kaplan's faith is unorthodox, but it's central to her life. She was raised Jewish, and although she claims no formal religion now, she prays and meditates every day. She believes God is keeping the virus at bay and that her faith is the reason she's alive today. "Everything starts from a thought, and then the thought creates a reaction," she says. "And I have the power to control my mind, before it gets to a physical level or an emotional level." Kaplan has never taken medicine, yet the disease has not progressed to AIDS (and she is not part of the population that has a mutation in the CCR5 gene that prevents progression of HIV to AIDS).

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