1. A computer-implemented method, comprising: providing, by one or more computing systems configured to provide a program execution service, a first group of multiple computing nodes that provide a program execution capacity at a first time for executing one or more software programs for a user; identifying, by the one or more configured computing systems and in response to determining that a change to availability of one or more computing nodes of the first group has occurred, multiple events that occur between the first time and a later second time and that each are capable of resulting in a modification of the program execution capacity being provided by the multiple computing nodes of the first group; determining, by the one or more configured computing system, whether to attribute one of the multiple identified events as a cause of the availability change; and if it is determined to attribute the one identified event as the cause of the availability change, providing, by the one or more configured computing systems, an indication of the one identified event as the cause of the availability change, and otherwise providing an indication of the multiple identified events as the cause of the availability change.