Variable inclusion in the registry was defined by a panel of US and international COPD experts using a modified Delphi method. This method is a process of anonymous voting which assumes that a group decision is more valid than a decision made by an individual. It comprises of three rounds to gather anonymized opinions on the core variables. The advantage of this process is the anonymity of participants which ensures that all opinions are considered equally, enabling views to be changed without inhibition by participants.
