Why do the published data fail to clarify the relationship between gastroesophageal reflux and asthma?

The relationship between gastroesophageal reflux (GER) and asthma has troubled physicians for centuries and has been a source of debate among pulmonologists, allergists, and gastroenterologists for decades. Attempting to tie together the pieces of the puzzle, numerous investigators have struggled to show that in patients with asthma, GER symptoms occur too frequently, gastric acid dwells for too long in the esophageal lumen, and refluxed gastric acid injures the esophageal mucosa more than expected. Unfortunately, all of the work done by these fine investigators has failed to demonstrate a "cause and effect" relationship. Although they have succeeded in convincing us that GER occurs more frequently in asthmatics than in nonasthmatics, they still must continue until we all know how to predict which patients have gastroesophageal-induced or gastroesophageal-exacerbated asthma.