1. A computer-implemented method of labeling items comprising: issuing, over a communications network, a labeling task to a plurality of workers participating in a crowdsourcing system; receiving, over the communications network, labels assigned to the issued task by two or more of the workers; sending the received labels and task data to inference components arranged to jointly infer both worker characteristics and characteristics of worker communities of which the workers are members, by assuming relationships between workers; and receiving inference results from the inference components, the inference results comprising an aggregated label for the task, the aggregated label taking into account the inferred worker characteristics and the inferred worker community characteristics.