• Decision-making;
  • Collective behaviour;
  • Deneubourg model;
  • Animal groups;
  • Human groups

We review and extend theoretical and empirical studies of how groups make decisions using combinations of private information and preference copying. We give six tested or testable predictions arising from models: (i) group decisions involve both true and false cascades; (ii) a small number of leaders can heavily influence a decision; (iii) individuals in groups make accurate and fast decisions; (iv) irrelevant alternatives change preferences; (v) optimal group size depends on the number of options; and (vi) pairs of higher quality options are more difficult to distinguish than lower quality options. We discuss our approach in the context of human organisations. Copyright © 2012 John Wiley & Sons, Ltd.