Priors gained from expert opinion can be the key to effective decision-making. Yet, there is continuing controversy with its use because of its subjective and potentially biased nature. I examine the use of expert opinion through four environmental case studies in which one or more experts participated in an elicitation exercise to provide inference on ecological problems. In each case study, I examine how expert opinion informed the model and the potential pitfalls that could result, especially in data-limited situations.
I discuss two opposing schools of thought: (1) experts provide a valuable source of information that can offer useful insights into a model and (2) expert priors are most times biased, leading to incorrect results and bad decisions. I show that expert opinion has a place in ecological analyses if carefully structured in a model. In situations in which data are limited or simply not available, steps can be taken to ensure its proper use and interpretation from models so decisions can be made urgently and updated when new data becomes available. Copyright © 2011 John Wiley & Sons, Ltd.