  We conduct an experimental analysis of a dataset comprising over 27 million
microtasks performed by over 70,000 workers issued to a large crowdsourcing
marketplace between 2012-2016. Using this data---never before analyzed in an
academic context---we shed light on three crucial aspects of crowdsourcing: (1)
Task design --- helping requesters understand what constitutes an effective
task, and how to go about designing one; (2) Marketplace dynamics --- helping
marketplace administrators and designers understand the interaction between
tasks and workers, and the corresponding marketplace load; and (3) Worker
behavior --- understanding worker attention spans, lifetimes, and general
behavior, for the improvement of the crowdsourcing ecosystem as a whole.
