Impact assessment (IA) is an important preoccupation of much evaluation in the STI policy field, as shown by country responses to the OECD STI Outlook policy questionnaire 2014 (). Through IA exercises, policy makers aim to better understand, identify and often quantify the causal relationships that link inputs (e.g. investments in R&D) to different actors (e.g. ministries, R&D agencies, firms) and to their impact on output and outcome measures (e.g. economic growth, improvements in health, environmental and living standards or broader societal changes). The rationales for such assessments include: to fine-tune and improve existing policy interventions; to inform spending priorities and focus future policy interventions on areas with the greatest expected impact; and to hold actors accountable for their performance and spending.