Severe asthma: Comparison of different classifications of severity and control.

•The definitions of asthma severity and control have changed over the last 20 years.•The agreement between ERS/ATS 2014 and ATS 2000 classifications is good.•The agreement between WHO classification, ATS and ERS/ATS classifications is poor.•The agreement between asthma control by GINA 2012 and GINA 2014 is poor.•Classifications of severity and control are arbitrary and subjective, thus variable.