E, the second another (as yet unannounced) compound suspected of having anti-Alzheimer's properties, and the third an inert placebo as a control.

ECONOMIST: Disposing of dementia

The curcumin arthritis studies have a major flaw: Neither included a placebo, or control group, says rheumatologist David Felson, who directs an arthritis research team at Boston University School of Medicine.

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One such, carried out in the British city of Durham, was controversial in that it was funded by a maker of children's omega-3 supplements and did not include a control group being given a placebo.

ECONOMIST: Eat your way to a better brain

The result was that three-quarters of the treated group did not relapse into depression: a success rate twice as high as that of the 20 patients in the control group, who received a placebo regimen.

ECONOMIST: People, like all living things, are four dimensional

Unfortunately, most of the studies that came to these conclusions were flawed: many results were anecdotal, and control groups were not established to take account of the placebo effect.

ECONOMIST: LSD

In the double-blind, randomized control trial, half the women got tenofovir gel and half got a placebo.

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But early studies reporting positive results for the vertebroplasty procedure did not have control groups, making it unclear whether the purported benefits were simply due to the placebo effect or the natural tendency of chronic pain to subside over time.

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And in a study published last year, researchers in Australia showed in a double-blind, placebo-controlled trial that subjects with suspected gluten sensitivity had substantially fewer symptoms on a gluten-free diet than control subjects who unknowingly ingested gluten.

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