When do we need more data? A primer on calculating the value of information for applied ecologists

1. Applied ecologists continually advocate further research, under the assumption that obtainingmore information will lead to better decisions. Value of information (VoI) analysis can be used to quantify how additional informationmay improve management outcomes: despite its potential, this method is still underused in environmental decision-making. We provide a primer on how to calculate the VoI and assess whether reducing uncertainty will change a decision. Our aim is to facilitate the application of VoI by managers who are not familiar with decision-analytic principles and notation, by increasing the technical accessibility of the tool. 2. Calculating the VoI requires explicit formulation ofmanagement objectives and actions.Uncertainty must be clearly structured and its effects on management outcomes evaluated. We present two measures of the VoI. The expected value of perfect information is a calculation of the expected improvement inmanagement outcomes that would result fromaccess to perfect knowledge. The expected value of sample information calculates the improvement in outcomes expected by collecting a given sample of new data. 3. We guide readers through the calculation of VoI using two case studies: (i) testing for disease when managing a frog species and (ii) learning about demographic rates for the reintroduction of an endangered turtle.We illustrate the use of Bayesian updating to incorporate new information. 4. The VoI depends on our current knowledge, the quality of the information collected and the expected outcomes of the available management actions. Collecting information can require significant investments of resources;VoI analysis assistsmanagers in deciding whether these investments are justified.