Characteristics of publications included in the systematic review
| Variables and categories | n (%) |
| Study approach | |
| Comparing urban vs rural areas | 59 (89) |
| Comparing cities or settlements | 5 (8) |
| Comparing intraurban variation | 2 (3) |
| Region | |
| Asia | 22 (33) |
| Africa | 22 (33) |
| Latin America | 21 (32) |
| Easter Europe | 1 (2) |
| Study design | |
| Cross-sectional | 58 (88) |
| Ecologic | 7 (10) |
| Cohort | 1 (2) |
| Methodology | |
| ISAAC | 34 (52) |
| Other | 32 (48) |
| Asthma definition* | |
| Wheezing ever | 19 (16) |
| Current wheeze | 42 (35) |
| Doctor diagnosis | 24 (20) |
| Exercise challenge test | 10 (8) |
| Self-report asthma | 15 (12) |
| Questionnaire diagnosis | 11 (9) |
| Age category (years) | |
| Children (0–12) | 15 (23) |
| Adolescent12–18 | 13 (18) |
| Children and adolescent (0–18) | 21 (34) |
| Adult (>18) | 9 (14) |
| All ages | 7 (11) |
| Year of the publication | |
| Before 1990 | 2 (3) |
| 1990–1999 | 6 (9) |
| 2000–2009 | 23 (35) |
| 2010–2017 | 35 (53) |
*Some studies used two or three asthma definitions, so percentages were calculated using the total number of definitions as denominator.
ISAAC, International Study of Asthma and Allergies in Childhood.