Table 10 The effect of considering publication bias when judging quality of evidence

Publication bias

In our review, we identified research evaluating whether female (rather than male) sex can increase the risk for persistence of headache over time. Four longitudinal studies [28, 37–39] at an early phase of investigation, explored this potential factor in multivariate analyses. All these studies explored the effect of female sex while including important potential confounders in the multivariate model. While Stanford and colleagues [38] reported female sex to be a significant risk factor when sex was entered simultaneously into the model with other co-variables (for example, anxiety, self-esteem, stressful life events), Monastero and colleagues [37], Termine and colleagues [39] and Wang and colleagues [28] reported no effect when adjusted for potential confounders such as age, medication overuse, age of onset, and psychiatric comorbidities. We considered this association explored by an adequate number of studies, and since we already downgraded for early phase of investigation we decided not to downgrade the quality of this evidence for publication bias.