Numbers can lie

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Study guide for research

It can be hard to make sense of the blizzard of studies on vitamins, diet, lifestyle and health risks that roll off the presses almost daily. It can be an even trickier call to decide whether to change one's habits as a result of the latest findings. Here are a few tips from experts to help you assess the research.

* Replication. Don't change your lifestyle just because of one study. The next one might show the exact opposite. You want to see studies replicated.

* Size of the effect. If a study reports that eating 10 rutabagas daily lowers your risk of ingrown toenails by 0.05%, that might not be a reason to go hog wild on rutabagas.

In the case of epidemiology studies, researchers suggest that you look for at least a doubling or a halving of an effect.

But also keep in mind that the absolute risk is important -- doubling the very rare risk of being struck by lightning, for example, is not very significant.

* Give randomized, controlled trials more weight. Many experts consider these more reliable than observational studies.

* Statistical significance. The finding should be statistically significant for you to pay attention to it. A "trend," although interesting, isn't enough.

* Size of the study. Bigger is better. A study that only looks at 20 people is likely less reliable than one that includes 20,000 people.

* Length of follow-up. Generally, the longer time a study tracks people, the more reliable the results will be, and the more likely it will be to detect an effect.

* Consistent findings. The more precise the results within a study, the better. Take, for example, a study that finds that a treatment extends life 50 days. If the study's 95% confidence interval (a statistical measure of precision) is a tight 45 to 55 days, it should be taken a lot more seriously than if the confidence interval is a loose zero to 100 days. In the latter case, the actual life extension could easily be zero days.

* Where was it published? Some researchers say that top journals are more likely to reject most unreliable studies. But beware: Such journals also tend to publish "surprising" studies that show something for the first time.

So, once again: Wait for other studies that show the same thing.

--Andreas von Bubnoff