2.2 Data Extraction
The data extracted from studies that met the inclusion criteria included the location of the study, the year of the study, sample size, mean age of the respondents, GFR-formular used, prevalence and risk factors, (in studies that carried out multiple logistic regression). In case the full text revealed that not all requirements were present, the paper was excluded. Additional literature was obtained through searching references in the manuscript (snowball method). An individual paper was categorized into different areas. The review was further elaborated by addressing each area separately and rereading all article that were relevant for that area.