Reverse spin bias: preliminary observations of reporting bias in medical systematic reviews

While conducting an umbrella review of e-cigarettes for smoking cessation, we observed that in many instances, systematic review authors reported findings favorable to the treatment, yet they declined to recommend it or recommended against it despite the evidence of its effectiveness in their own systematic reviews.

We searched the literature for a term or category to describe this form of reporting bias where the authors' recommendations dismiss their findings of treatment benefit. Ideally the term spin bias should apply to any conclusion or recommendation not supported by the findings of the study, but in practice spin bias is almost exclusively applied to the narrative attribution of significance or causation to statistically non-significant data or findings.

After observing that many systematic review authors dismissed their findings of effectiveness for e-cigarettes for cessation, we wondered if this form of reporting bias also occurs in the systematic reviews on other controversial treatments. We made a rapid search for recent systematic reviews on medical cannabis for pain, another controversial treatment. Here also we observed that many authors did not recommend cannabis for pain management even though their findings clearly showed treatment benefit. We tentatively offer the term reverse spin bias for the narrative discounting or dismissal of statistically significant findings. We catalogued the narrative turns that enabled reverse spin bias in 20 systematic reviews of e-cigarettes for cessation and medical cannabis for pain. We identified five mechanisms: discount the evidence base, discredit the primary studies, appeal to fear, dismiss the treatment modality a priori, and omit findings. We speculate that authors introduce reverse spin bias to improve their chances for publication or to support their position about a treatment.

A standard task for editors and peer reviewers is confirming that treatment recommendations are supported by the review's data, yet our examples strongly suggest that this examination for reporting bias is frequently skipped. By proposing a new term, reverse spin bias, we hope to bring stronger scrutiny to bear on these instances of reporting bias that are detrimental to evidence-informed clinical practice.