Inequality of opportunity in selection procedures limits diversity in higher education: An intersectional study of Dutch selective higher education programs

Methods For this study, we used the STROBE cohort reporting guidelines [43] and the SAMPL guide- lines [44]. These are statistical and methodological guidelines suited to the type of study we executed. Study design, setting and eligibility criteria, study size We conducted a retrospective multi-cohort study using anonymized non-public microdata from Statistics Netherlands, focusing on applicants and students in academic years 2019–2020 and 2020–2021. These years were chosen, as they were the two most recent years for which essential variables were available in Statistics Netherlands microdata at the start of the research. Statistics Netherlands does not allow for analysis on single-institution data. Therefore, we cre- ated several clusters of studies which each consisted of at least three institutions, to make data non-traceable to any particular institution. In cases where different studies had to be combined to achieve this, clusters were made on the basis of similarity of programs (e.g., related to per- sonal healthcare or not). Table 1 contains information on the study programs in all HBO clus- ters (starting with ‘SH’) and all university clusters (starting with ‘SU’). The six HBO clusters included 19 HBO study programs, the nine university clusters included 28 study programs. We only included study programs taught at HEIs which are pub- licly funded and which are members of either the Netherlands Association of Universities of Applied Sciences (Vereniging Hogescholen) or Universities of the Netherlands (Universiteiten

van Nederland), as these are the organizations which granted us permission to perform data analysis on their anonymized applicant pool and student population. It is important to note that many selective programs (e.g. Nursing) are only selective at one or a few HEIs, but that students can enroll in these programs at other HEIs without having to go through a selection procedure. Therefore, S1 Table also contains information on the number of HEIs that did not use selection for the particular study programs. Since this research focuses on inequality of opportunity in selection, the student populations of non-selective programs are not included in our analyses. We only used the term ‘selective program’ for programs which have a capacity limit and use selection to decide which applicants to admit for the limited places available. We created the following groups: Applicants for selective programs (N = 85,839). This group consists of all domestic applicants who applied through Studielink (the national online application portal for post-sec- ondary education in The Netherlands) for at least one selective program, and who received a ranking number. The group is divided into HBO applicants and university applicants. Appli- cants who never received a ranking number (e.g., because they decided to withdraw from the selection procedure, or were not eligible) were not included, since the selection committee was not able to offer them a place (see Fig 1). Age cohort (N = 204,075). To compare the demographics of study clusters with the

demographic characteristics of the young population, we used Statistics Netherlands micro- data of all 16-year-olds who were registered in The Netherlands on October 1st in 2015. Within the age cohort, we also distinguished whether 16-year-olds were higher general or pre-univer- sity students, since these are the most common educational routes to HBO and university. Data sources Studielink provided all applicant data of all selective HE programs from 2019 and 2020 to Sta- tistics Netherlands, which pseudonymized the Citizen Service Numbers (CSN) of domestic applicants. The researchers used pseudonymized CSN to merge other Statistics Netherlands microdata to the dataset. International applicants were excluded from this research. PLOS ONE Inequality of opportunity in Dutch selection procedures limits diversity in higher education PLOS ONE | https://doi.org/10.1371/journal.pone.0292805 October 13, 2023 5 / 24