In these questionnaires the latest available information from previous updates was typically verified and updated by government officials. This information was then integrated through national and international secondary sources (see, for example, Grubb and Wells, 1993, Annex 1, OECD, 1999, Annex 2.A). Labour legislation was used as the main source of information only in the case of the few non-member countries (see Venn, 2009, Section 2) or in specific cases whose interpretation was particularly difficult (see OECD, 2004).