Characteristics of studies included in the systematic review

Study characteristicsStudies# n
Year of publication
 Before 200030
 After 201038
Level of analysis
 Area level14
 South America61
 North America46
Sample size
 5001–10 00026
 10 000–100 00030
 >100 0006
Age category
 Children (<18 years old)119
Health outcomes
 Allergies or allergic reactions31
 Allergic rhinitis (i.e. hay fever)22
 Atopic dermatitis (i.e. eczema)27
SEP measures
 Parental or own education level79
 Individual or household income76
 Occupational level or employment status43
 Area-level deprivation or poverty22
 Housing characteristics19
 Country-level SES10
  • For a complete overview, see the online supplementary material. SEP: socioeconomic position; SES: socioeconomic status. #: total may exceed 183 as some studies covered multiple regions and used multiple health outcomes and SEP measures; : only most common SEP measures included in table.