What Do Scientific Studies Show? How seriously should we take them?

Gary Gutting in the New York Times:

As any regular reader of news will know, popular media report “scientific results” nearly every day. They come delivered in news reports and opinion pieces, and are often used to make a variety of points concerning important matters like health, parenting, education, even spirituality and self-knowledge. How seriously should we take them?

For example, since at least 2004, we have been reading about studiesshowing that “vitamin D may prevent arthritis.” A 2010 Johns Hopkins Health Alert announced, “During the past decade, there’s been an explosion of research suggesting that vitamin D plays a significant role in joint health and that low levels may be a risk factor for rheumatologic conditions such as rheumatoid arthritis and osteoarthritis.” However, in February 2013, a more rigorous studycalled the previous studies into serious question. Similarly, despite many studies suggesting that taking niacin to increase “good cholesterol” would decrease heart attacks, a more rigorous studyshowed the niacin to have no effect.

Such reports have led many readers to question the reliability of science. And given the way the news is often reported, they seem to have a point. What use are scientific results if they are so frequently reversed? But the problem is typically not with the science but with the reporting.

More here.