I am a graduate student doing research on COPD and am having difficulty in classifying patients who have quit relatively recently versus those who have been smoke-free for a much longer period of time.
I have come across multiple definitions on how to classify these patients. For example, The CDC classifies anyone who has quit smoking prior to being asked the question as an ex-smoker, while other authorities state that they only classify patients ex-smokers if they have been smoke free for a month. Even then there are others that classify ex-smokers in two categories, those who have stopped smoking for over 12 months, and those who haven't.
Is there a standard definition for this classification? Any sources would be much appreciated.