As a manuscript editor and freelance manuscript editing coordinator for the JAMA specialty journals, I am constantly having to edit out cause-and-effect language from observational studies that are not randomized clinical trials. According to the AMA Manual of Style, the word effect, as a verb, means to bring about a change; as a noun, it means result.
A randomized clinical trial is one of the few types of studies that are designed to assess the efficacy of a treatment or intervention (and thus allowed to use cause-and-effect language) because the participants are treated in controlled, standardized, and highly monitored settings.
Whenever I come across a study in which the authors are trying to determine, for example, whether the use of a certain type of drug will reduce the risk of some complication following a certain type of surgery, I need to verify whether the study is a randomized clinical trial or a report of a controlled laboratory experiment. If it isn’t, and is a report of an observational study (such as a cohort, cross-sectional, case-control, or case series study, or a meta-analysis), then all cause-and-effect language must be replaced. But by what?
Generally, association may be a useful replacement for effect. The AMA Manual of Style defines association as a “statistically significant relationship between 2 variables in which one does not necessarily cause the other. When 2 variables are measured simultaneously, association rather than causation generally is all that can be assessed.” So instead of saying the “effect of this on that,” rephrase as the “association of this with that” or the “association between this and that.”
Sometimes, however, the authors don’t agree and want me to change it back, in which case I calmly let the authors know that it is AMA style to allow cause-and-effect language only for randomized clinical trials and controlled laboratory experiments and that, perhaps in the “Discussion” section of their manuscript, they can try to make arguments to support that the association might be causal. However, to quote from one of our scientific editors, “the expression and ultimate interpretation of the findings can’t be causal.”
The use of cause-and-effect language is quite common in everyday speech, and so it is easy for most people to assume that if one event comes before another, then the first is the cause of the second. In the JAMA Network journals, findings that rely on this type of logic had to have been rigorously tested in a randomized clinical trial.—Paul Ruich