Interesting question, but I am afraid that there is no definitive answer because of the way the prevalence studies are conducted. The incidence of mild, moderate, and severe asthma varies considerably from one study to the next. You are therefore not able to cite a single percentage that accurately estimates the frequency of any of the three classifications.

An article in “Allergy” from 2007 states that the incidence of mild asthma ranges from 50 to 75% of asthmatic patients, suggesting that moderate asthma is less than 50%. 

Probably the most definitive answer comes from the 2012 Asthma:Outcomes and Treatment Regimens study which suggests that 46.3% of asthma patients had moderate disease; 51.3% had severe asthma and 2.4% had mild asthma (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3622643/#!po=14.8649).

I hope this helps

Wilmore

http://www.ncbi.nlm.nih.gov/pubmed/17508962

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3622643/#!po=14.8649

thankyou....theAIMstudyandtheCDCsurveilancestudyessentiallysupportwhatyousaid.R

helpful.;....thank you......

Another paper with data on moderate asthma epidemiology:

Eur Respir J. 2000 Nov;16(5):802-7.

Clinical management of asthma in 1999: the Asthma Insights and Reality in Europe (AIRE) study.

Rabe KF, Vermeire PA, Soriano JB, Maier WC.

Thanks Calman this helped