The number of workers across skill-groups and within a sector is identified under the assumption that within sectors, workers engage in the same amount of hours across the different labour categories (high-skilled, medium-skilled and low-skilled).35 In the second step, to calculate a wage for each of these worker categories, the value added of a given worker category (the wage bill) is divided by the number of workers in that category and sector. The resulting output is an average wage rate for each of the three categories of workers within a sector giving rise to a maximum of 105 country-sector-skill category-year wage observations.36 This information is then used to calculate aggregate measures of wage inequality37 — a Gini coefficient—using weights capturing the number of workers across skill categories and sectors within a country (Box 2). Great care has been taken to harmonise cross-country measures of inequality by the OECD in the Income Distribution database (which does not suffer from the problem of using income and expenditures in different years).