“…Therefore, including children with previous respiratory diseases could evolve into sampling (selection of individuals), confounding (proven impact on outcomes) or information bias (previous knowledge of an existing problem). In this context, 66.7% (22/33) [ 12 – 15 , 17 – 21 , 25 , 26 , 29 , 32 – 37 , 39 – 42 ] of the studies excluded individuals with respiratory diseases, 27.3% (9/33) [ 16 , 22 – 24 , 27 , 28 , 30 , 31 , 38 ] did not mention respiratory diseases as a factor of exclusion or non-inclusion, and 6% (2/33) [ 11 , 43 ] excluded only individuals with a history of smoking. Among the studies that excluded previous respiratory diseases, several exclusion criteria could be observed: some authors excluded only individuals with exacerbation of asthma or cough; others excluded any respiratory conditions that might impair the evaluation; and others used standardized instruments such as the ISAAC questionnaire (The International Study of Asthma and Allergies in Childhood).…”