There are literally thousands of ways to design a study. When a news story suggests, "A new scientific study has found…" or a celebrity doctor begins a sentence with, "Studies show…", you need to ask, "What kind of studies?" Because "studies" are not equally reliable, they all have different limitations, and they should not be acted on in the same manner — or even acted on at all. Here's a quick guide to understanding study design that will help you navigate the often bewildering world of health research.
The one chart you need to understand any health study
Today’s study is just the latest word and must be interpreted in context of others.