Introduction 11 Wright, 2013; Nishii & Wright, 2007; Piening, Baluch, & Ridder, 2014; Snape & Redman, 2010). On the other hand, HRM initiatives may have more impact when implemented for certain employee categories. The impact would be greatest when HRM investments are focused on strategic job positions and the employees in these positions (Huselid & Becker, 2011). The performance of employees in such positions is relatively important for the performance of the overall organization, either through reduced cost or through increased revenue. Hence, any HRM investment in these jobs and employees will have a relatively high potential payoff. In practice, many contemporary organizations already differentiate their HRM investments; for instance, by distinguishing talents or high potentials within their employee populations (see Chapter 6). Overall, there is evidence for contextual influences on the impact of HRM, both between and within organizations. 1.1.2 Evidence-based HRM What does the above scientific discourse imply for local HRM departments and the ways in which they manage the human capital of their employees? With a vast body of scientific literature on what constitutes effective HRM, it should be clear which HRM policies and practices should be implemented. Yet, faulty practices are abound in HRM as decisions are frequently based on personal preferences, unsystematic experiences, knee- jerking, fad chasing, and guesswork regarding what works (Rousseau, 2006; Rousseau & Barends, 2011). Fortunately, there is increased interest in evidence-based decision-making in HRM. Evidence-based management involves “translating principles based on best evidence into organizational practices ” (Rousseau, 2006, p. 256). According to Rousseau and Barends (2011), good evidence-based management combines four sources of information: (1) practitioner reflection and judgement, (2) stakeholders concerns, (3) scientific evidence, and (4) reliable and valid organizational metrics. The first two sources of information are nearly always present in the contemporary HRM function: HRM professionals are designing policies and practices in light of business, line management, and employee needs and the legislative context. The third source of information has become more important over the course of time. Currently, a strong basis of scientific evidence exists for what kind of HRM principles should work, built on the academic studies conducted in fields such as industrial, occupational, organizational, social and/or behavioral psychology, and general management and HRM research (Briner, 2000; Cascio & Aguinis, 2010; Charlier, Brown, & Rynes, 2011; Kaufman, 2010, 2014; Locke, 2009). The greatest deficit of the contemporary HRM function lies in the fourth source of information: HRM departments often lack the capability – both in skills and metrics – to measure and quantify the strategic contribution of their HRM activities, its bottom-line impact, and any progress therein in the own, local organizational context (Cascio & Boudreau, 2010; Paauwe & Farndale, 2017).