The collection of 21 African impact assessment studies within a set of covers is itself a valuable contribution. Published efforts to measure the potential and actual returns to agricultural research investment in Africa remain few and far between. The case studies illustrate differences in the levels of analysis – from local to national to international – and the time lags involved to capture impact at these different levels. They also illustrate differences in methods of analysis, and in outcomes. The fact that the book was published in 2007 and the case studies in the main refer to research undertaken prior to 1995 illustrates the time lag often involved for results to find their way into wider use when impact can be studied. In its three general chapters the book argues the need for more measurement of the impact of science and in this sense falls short of that implied in its perhaps pretentious title.

There are three ‘overview’ chapters: Chapter 1 addresses the challenges facing African agriculture; Chapter 2 describes the roles of impact assessment in evaluating agricultural investments; Chapter 24 is a very useful review of impact assessment methods and operational decisions in planning and implementing studies. While this final chapter brings out the need for careful choices to fit the particular circumstances under study, the book would have been stronger if the choice of method had been related to the various applications of impact information, which differ widely in the timing required for useful feedback. It can be argued that impact studies have themselves had very little impact due to mis-matches between the appropriate timing for the study and the actual timing of the decision cycle of their various applications.