Fig. 2

Proportion and number of included studies with available and accessible (meta-)data infrastructure (total n = 16). Study-specific internet-accessible portals (through which data documents are often accessible) were considered as (meta-)data infrastructure. Available if the existence of a (meta-)data infrastructure was identified through the study website and/or data document search; accessible if contents could be viewed without registration or registration. (a) Credentials needed, no registration option. (b) Corresponding to (meta-)data access infrastructure not available.