classEx - an online tool for lab-in-the-field experiments with smartphones

classEx is an online tool for running experiments with smartphones. It can be employed for lab-in-the-field experiments, allowing the investigation of behavior in natural settings and with large groups, even if their size is unknown and varying. Standard experiments with multiple treatments, monetary incentives, roles, groups, rounds and stages are available in a ready-made format. An easy-to-use modular backend system allows users to conveniently implement their own experiments. Replication is facilitated by the possibility of sharing experiments and results with other researchers. We provide some applications, describe the functionality and show how classEx tackles the challenges of lab-in-the-field research. (C) 2019 Elsevier B.V. All rights reserved.