The capacity coefficient has become an increasingly popular measure of efficiency under changes in workload. It has been used in applications ranging from psychophysical detection tasks to complex cognitive tasks, as well as in addressing questions in social and clinical psychology. The basic formulation compares response times to each stimulus property (or task) in isolation to response times with all stimulus properties (or tasks) at the same time. A number of variations on the basic capacity coefficient have been used, both in the experimental design and in the calculations, and many more are possible. Here we outline the theoretical reasons for the different variations and discuss the information researchers need to choose the appropriate variation of the capacity coefficient. We then compare the different analyses applied to two cognitive tasks: an audio-visual detection task and a dual n-back task.