Causal diagrams, gastroesophageal reflux and erosive oesophagitis.

Gastroesophageal reflux and its consequences have inspired numerous research questions in recent years: are non-erosive reflux disease (NERD) and erosive oesophagitis phenotypic expressions of gastroesophageal reflux disease? Why do patients with NERD not respond to treatment as well as patients with erosive oesophagitis? What is the natural history of NERD? Causal diagrams, coupled with conditional probabilities, offer clear and surprising answers.