Second, the review was meant to take a cross-national approach, thus aimed explicitly at retrieving studies from countries other than the United States. Hence, search terms related to the continents or regions were added, specifically for South America, Africa, Asia and the Middle East. Additional relevant literature was elicited from participants of the OECD ECEC Network meeting on 4 July 2017. Moreover, feedback and suggestions provided by interested and participating countries in the Policy Review project from September to November 2017 were also integrated in the literature review.
Third, to ensure the inclusion of grey literature in addition to scientific papers, policy and research reports from several countries were covered (e.g. Australia, Flemish Community of Belgium, the Netherlands, England [United Kingdom], and the United States) through search engines as Google and Google Scholar. This allowed the consideration of (ongoing) research projects such as the Effective Early Education Experiences (i.e. E4kids) study in Australia and Measurement and Monitoring of Quality (i.e. MeMoQ) study in the Flemish Community of Belgium, for which scientific papers are not yet available. Moreover, several policy reports were used to collect information on specific structural features, such as the Quality Rating and Improvement Systems (QRIS) in the United Sates that contained highly relevant findings.
Lastly, the literature review took a comprehensive approach to study the relations between structural and process quality including centre- and family-based day care and focused on the age range from birth up to five years of age.