2.1. Data Extraction

From the studies included in the sample, data relevant to the present review were extracted, and registered the variables aim of study, design, sample characteristics (including gender, age, and nationality), measures of SES, and outcome/conclusions.

Next, the various measures of SES were categorized by education, income, occupation, neighborhood or other if none of the mentioned categories pertained. In addition, less precisely defined variables (e.g., when income was dichotomized as low or high) were registered. Measures of PA were registered according to the four valid measurement dimensions (i.e., duration, frequency, intensity, type, or mode of PA). Phrases similar to “for at least 30 min at a time” were coded as duration. The question of whether the exercise could be regarded as vigorous or moderate was recorded as a measure of intensity. In some studies, authors had pre-calculated intensity by type of PA, particularly when the terms “moderate” and “vigorous” activity were used or when Ainsworth’s code schemas, which classify specific PA by rate of energy expenditure as the Metabolic Equivalent for Tasks (METs) [14], was cited.