Second, the demand for evaluation has expanded because OECD countries have increased public investment in R&D despite budget constraints. However, it is difficult to determine and measure the various impacts of public R&D and the most important challenges are discussed in Box 5.4. Over the past decade, national governments and academics have developed new analytical techniques for assessing the impacts of public R&D investment, such as econometric analysis, data linkages approaches and case studies. Further work is needed on integrating different approaches and methodologies to create coherent impact assessment practices (OECD, 2008a).