1. One or more computer-readable media storing computer-executable instructions that, when executed on one or more processors, perform acts comprising: selecting a first set of elements from a group of elements for labeling by one or more human users; receiving a label of each element of the selected first set of elements from the one or more human users; determining a distribution of the group of elements relative to a distribution of the selected first set of elements; training a model based at least in part on: (i) the received labels of the selected first set of elements, and (ii) the distribution of the group of elements relative to the distribution of the selected first set of elements; selecting a second of elements from a group of elements for labeling by one or more human users, the selecting based at least in part on the distribution of the group of elements relative to a distribution of the second set of elements; receiving a label of each element of the selected second set of elements from the one or more human users; training a model based at least in part on: (i) the received labels of each element of the selected second set of elements, and (ii) the distribution of the group of elements relative to the distribution of the selected second set of elements; and repeating the selecting of a set of elements, the receiving, and the training until a trained model satisfies a stop condition.