Duration-based IOA is centered on the premise the behavior recorded is likely to occur for extended periods of time. Total duration IOA is a feasible option to measure agreement among data collectors for such behaviors.
When using total duration IOA, data collectors record the amount of time the behavior occurs. At the end of the observation period, both data collectors add the duration of each occurrence together. Total duration IOA is calculated by using the shorter time as the numerator and the longer time as the denominator. For example, if the two times recorded were 15 minutes and 20 minutes, the percentage agreement would be 75%.