Science is easy; explaining it is hard. Back in 2009, Evidence Soup recommended the excellent Health News Review, whose mission is to "hold health and medical journalism accountable" (more about them at the end of this post). They've published Tips for Understanding Studies (available for purchase here). One of their free online writeups is a must-read for anyone working with evidence. Yes, it's basic -- but depending on your level of experience, will be a valuable refresher, an intro to research methods, or a guide to science writing.

Does The Language Fit The Evidence? – Association Versus Causation was put together by Mark Zweig, MD, and Emily DeVoto, PhD, "two people who have thought a lot about how reporters cover medical research". (I've been acquainted with Emily DeVoto for several years; I like that her catchphrase is "The plural of anecdote is not data.").

Passive language vs. active voice. The authors describe how an 'association' can be inadvertently misconstrued as a cause/effect relationship:

"A subtle trap occurs in the transition from the cautious, nondirectional, noncausal, passive language that scientists use in reporting the results of observational studies to the active language favored in mass media.... For example, a description of an association (e.g., associated with reduced risk) can become, via a change to the active voice (reduces risk), an unwarranted description of cause and effect. There is a world of difference in meaning between saying 'A was associated with increased B' and saying 'A increased B.'" [emphasis is mine]

These are subtle things with tremendous importance. When I was in school, I often heard "Correlation doesn't mean causation." Evidently, the difference is still be a big hurdle both for experts and non-experts. Zweig and DeVoto illustrate how things can go awry in this helpful example: