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Does The Language Fit The Evidence? - Association Versus Causation

by Mark Zweig, MD, and Emily DeVoto, PhD, two people who have thought a lot about how reporters cover medical research

A health writer’s first attempt at expressing results from a new observational study read, “Frequent fish consumption was associated with a 50% reduction in the relative risk of dying from a heart attack.” Her editor’s reaction? Slash. Too wordy, too passive. The editor’s rewrite? “Women who ate fish five times a week cut their risk of dying later from a heart attack by half.” This edit seems fair enough – or is it? The change did streamline the message, but with a not-so-obvious, unintended cost to the meaning. Was the subjects’ fish consumption really responsible for their dying less frequently from heart attacks? The new wording suggests that’s the case, but the original study does not support a conclusion of cause and effect.

Epidemiologic – or observational – studies examine the association between what’s known in epidemiologic jargon as an exposure (e.g., a food, something in the environment, or a behavior) and an outcome (often a disease or death). Because of all the other exposures occurring simultaneously in the complex lives of free-living humans that can never be completely accounted for, such studies cannot provide evidence of cause and effect; they can only provide evidence of some relationship (between exposure and outcome) that a stronger design could explore further. In other words, observational studies cannot distinguish direction--whether exposure A influences outcome B, or B influences A, or both are influenced by something else, even if that association may be strong and consistent. What other design could illuminate a causal nature and direction of the relationship, if present?

The only study design involving humans that does rise to the level of demonstrating cause and effect is a randomized trial. In this design, study subjects are assigned an exposure (or a control condition) at random, irrespective of any other exposures in their lives, and all such other exposures are then assumed to even out between the treated group and the control group of subjects (and this can be demonstrated). As a result, the only difference between the groups is whether they receive the exposure under study or the control condition. This approach is a true experiment. Any difference in outcome seen between the control and the experimental group should be due to the one factor or variable that differs.

Because observational studies are not randomized, they cannot control for all of the other inevitable, often unmeasurable, exposures or factors that may actually be causing the results. Thus, any “link” between cause and effect in observational studies is speculative at best.
In reporting on observational research, language here is crucial, because the audience may not be familiar enough with epidemiologic evidence and study design to appreciate the nuances.  To a general audience, language such as, “fish consumption is linked [or tied] to the risk of heart attacks” may sound causal even when a causal relationship is not warranted.

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. Active language is fine in general – who wants to write like a scientist? But problems can arise when the use of causal language is not justified by the study design.  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.” The difference may seem subtle in terms of language, but is large in terms of meaning.

Indeed, in practice, a shift to causal language can occur at any stage: writing, editing, or headline composing, with similar effects on meaning. Without attention to the underlying design of studies, distortions of wording can creep in that could lead readers to overestimate the meaning of a given study and possibly even make life choices that the evidence does not warrant.

Another problem for journalists may arise in the language that scientists themselves and others use to describe the results of observational studies. Sometimes even scientists and press-release writers slide into causal language in expressing results of observational studies. You may find that language in a scientific publication is carefully chosen for the conclusion in the abstract or in the text, but not used so strictly in the discussion section. Thus, borrowing language from scientific papers warrants caution.

News writers sometimes attempt to qualify results by using such words as “seems,” “may,” or “appears.” These words are intended to convey uncertainty, which is a healthy impulse when describing imperfect studies (i.e., most of them), but they still leave the reader with the idea that, however uncertain the results, the relationship between the exposure and the outcome is one of cause and effect.

Although much of our concern is with passive verbs that reporters convert to active, or with adjectives (“lower” risk) that reporters convert to verbs (“lowered” the risk), nouns that imply causation are another frequent problem. For example, “the protective effect,” “protection,” or “the benefit” often appears in reports about observational studies. We urge journalists to avoid such language. An alternative might be, “Persons who ate the most fish were observed to have fewer heart attacks. However to attribute this observation to fish consumption, rather than to some other factor in their lives, a randomized trial is required.”

What is the conscientious journalist to do? Part of the job of the health journalist is to understand the difference between the study designs used in epidemiologic versus experimental research, to look at the description of the study design – ideally from the original article –and then to choose appropriate wording to describe results in the news piece. For observational reports, wording could include a qualification about the meaning of the results (see “suggested language,” right-hand column of table). For example, “Experimental research is required before we can say that eating fish lowers the chance of dying from coronary heart disease.”  Or, “A trial that randomly assigns people to eat fish or not eat fish is required to demonstrate that it is fish eating that actually lowers the chance of dying from heart disease.” (The latter may be the better choice, because it is the randomizing process that most effectively eliminates other possible causes.)

The health journalist has an opportunity to add great value to the piece by offering context. Virtually all research occurs in the context of previous work. The meaning of new research is impossible to appreciate without taking into account existing research. There may be inconsistencies and uncertainties in the existing data, and possibly important controversies among scientists working in the field.

Because a single new study can rarely stand alone in what it means, we suggest that health journalists focus, where possible, on helping the audience understand the limits of the new research and how it fits into the existing body of knowledge. In our view, the journalist can add the most by providing balanced, thoughtful context. This will ultimately help the general audience better appreciate the scientific process and more fully grasp the meaning of new results.

CONCLUSION: An important part of reporting results of research in health news lies in attention to language that may in subtle ways imply cause-and-effect relationships, where the underlying study design does not warrant such language. We urge health care journalists to be mindful of when causal language is warranted by the study design and when it is not. Health journalists’ vigilance for these subtleties will result in more accurate communication of research findings to the public. This, combined with providing relevant context, will hopefully lead to the more scientifically literate audience that the editors of the New England Journal of Medicine sought in writing the 1994 editorial entitled, “Clinical Research – What Should the Public Believe?” (Angell M, Kassirer JP. NEJM 1994;331:189-190).

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