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Fortunately, the responsibility for providing evidence is on the part of
the person making the claim, not the critic. It is not the responsibility
of UFO skeptics to prove that a UFO has never existed, nor is it the
responsibility of paranormal-health-claims skeptics to prove that crystals
or colored lights never healed anyone. The skeptic's role is to point out
claims that are not adequately supported by acceptable evidcence and to
provide plausible alternative explanations that are more in keeping with
the accepted body of scientific evidence.
        -- Thomas L. Creed, The Skeptical Inquirer, Vol. XII,
         No. 2, pg. 215