Comparative studies show that in Germany there is a particular strong link between the educational system and the labour market. Allmendinger (1989) points out that the German educational system is highly stratified and standardized with nationwide quality standards facilitating employers to “rely on credentials to represent skill content reliably” (Müller & Shavit, 1998, p. 7). Germany’s dual vocational training system equips individuals with occupation specific skills and certificates play an important role: they indicate a specific set of skills to employers allowing them to allocate persons to corresponding jobs (Müller & Shavit 1998).

However, it is rather unclear which role general cognitive skills play on the German labour market. According to the OECD, skills like numeracy, literacy and problem solving are key-information-processing skills which “provide a foundation for effective and successful participation in the social and economic life of advanced economies” (OECD, 2013a, p. 52). There exists a huge body of evidence documenting that those skills are linked to full-time-employment and earnings as well as to individuals’ participation in community groups and voluntary activities (OECD & Statistics Canada, 2011). From an economic perspective referring to Becker’s (1964) human capital approach, skills are acquired on-the-job or by attending school. Education is regarded as an investment into an individual’s human capital and is rewarded on the labour market with higher earnings. In a competitive market wages are an indicator of individual career success depending on one’s abilities and competencies. To empirically analyse individual investments and rewards, Mincer (1974) proposed a simple regression model that empirically takes into account the human capital in the form of number of years spent in different educational tracks. However, in the last couple of years researchers demonstrated that replacing the ‘years of schooling’-variable by numeracy and literacy competency scores adds variance to the prediction of wages in the classical Mincer regression (e.g. Charette & Meng, 1998; Hanushek et al., 2013).

Referring to the task approach researchers demonstrated that wages are not only influenced by individual’s skills, but also by job tasks and requirements. Autor and Handel (2013) revealed that “abstract problem solving and creative, organizational, and managerial tasks” (p.S70) are linked to higher earnings than manual or routine tasks.

Consequently, both cognitive skills and tasks requirements should have an impact on employees’ earnings. In our paper, we would like to investigate if there is an additional wage premium for skills and educational certificates when performing complex tasks. Evidence for this interaction hypothesis is provided by Gottfredson (2004) who pointed out that “the advantages conferred by higher levels of g [general cognitive skills] are successively larger in successively more complex jobs, tasks, and settings” (p. 176). Meta-analytical findings could also find evidence for this idea (Salgado et al. 2003).

We would like to investigate interaction effects for skills and complex task requirements and certificates and tasks requirements. Since the German labour market relies strongly on certificates we hypothesise to find interactions mainly for educational certificates and complex tasks.

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