Causality and headache triggers

Abstract

Objective: The objective of this study was to explore the conditions necessary to assign causal status to headache triggers.

Background: The term "headache trigger" is commonly used to label any stimulus that is assumed to cause headaches. However, the assumptions required for determining if a given stimulus in fact has a causal-type relationship in eliciting headaches have not been explicated.

Methods: A synthesis and application of Rubin's Causal Model is applied to the context of headache causes. From this application, the conditions necessary to infer that 1 event (trigger) causes another (headache) are outlined using basic assumptions and examples from relevant literature.

Results: Although many conditions must be satisfied for a causal attribution, 3 basic assumptions are identified for determining causality in headache triggers: (1) constancy of the sufferer, (2) constancy of the trigger effect, and (3) constancy of the trigger presentation. A valid evaluation of a potential trigger's effect can only be undertaken once these 3 basic assumptions are satisfied during formal or informal studies of headache triggers.

Conclusions: Evaluating these assumptions is extremely difficult or infeasible in clinical practice, and satisfying them during natural experimentation is unlikely. Researchers, practitioners, and headache sufferers are encouraged to avoid natural experimentation to determine the causal effects of headache triggers. Instead, formal experimental designs or retrospective diary studies using advanced statistical modeling techniques provide the best approaches to satisfy the required assumptions and inform causal statements about headache triggers.

Figure 1

Three assumptions for causal inferences of headache triggers. To infer that a headache trigger causes a headache (or causes the processes that do), several assumptions must be satisfied during pairings (Time 1 versus Time 2) of a trigger (e.g., drinking wine) and its opposite (e.g., not drinking wine). A headache sufferer must be the same across pairings such that they are equally as likely to have a headache absent the trigger. The trigger and its effect must be the same across pairings such that future encounters are likely to have the same influence. The pattern of background triggers (black and white circles) must be equivalent across pairings such that other trigger effects are not mistaken for the candidate trigger (wine).