Scientific studies show. . .

“Scientific studies have shown. . .”

“Recent research suggests. . .”

“A study presented recently reported. . .”

These types of phrases are used daily in the popular media to report on medical and scientific studies which produce results the general population may find interesting. They’re also used regularly by those trying to convince you to buy certain products (e.g., supplements), follow certain diet plans, or take prescription drugs. Unfortunately, such references to scientific evidence are frequently misleading.

In medicine, there are many different types of studies and reports that are used as evidence to support a given treatment recommendation. The thing that most people (especially those writing media reports) don’t seem to realize is that some types of evidence are considered much stronger than others. Many times the media doesn’t seem willing or capable of distinguishing very weak evidence from very strong. Those who’re trying to sell you snake oil are much worse, and will often mislead you by using such phrases while really referring to virtually nonexistent or at least extremely limited evidence.

Some general categories of clinical medical evidence, presented from weakest to strongest, are reviewed below.

Anecdotal evidence. This is literally when recommendations are just based on the experiences of a few patients. A (more…)