Unlike similar efforts to assemble international indicators on the labour market, the process for the KILM project was not initiated by collecting information directly from national statistical sources. Instead, initial efforts concentrated on pulling together information directly from international data repositories. Whenever data were available from more than one data repository, the ILO performed a review of the data and background documentation from each repository in order to select those most suitable for inclusion in the database. Factors used in making the appraisal included general reliability of the sources providing the data, availability of notes regarding the scope of coverage, availability of gender and age statistics, and degree of historical coverage. Occasionally, two data repositories were chosen, and any resulting breaks in the historical series are duly noted.
Historical continuity is important in any presentation of a data series.
Without overburdening the data tables, it is necessary to alert users to significant changes in the source, definition or coverage of the data from year to year. An important feature of statistics is the ability they give to users to compare data for one country with similar data for another country. Thus, governments which notice a high youth unemployment rate in their country in comparison to a neighbouring country may wish to focus on studying policies aimed at employing youths in the other country and initiate a similar programme in their own country. In reality, however, international comparisons are not a simple matter. There are caveats relating to the methodologies of measurement that require time and effort to sort out before reasonable comparisons can be made.