Four basic types of IOA as described by Johnston and Pennypacker (2009): Total agreement - Smaller total ÷ Larger total X 100 = % Agreement Exact agreement - Total agreements ÷ Total number of intervals X 100 = % Agreement Interval agreement - Total agreements ÷ Total number of intervals X 100 = % Agreement Occurrence/nonoccurrence agreement - Total agreements ÷ Total number of intervals X 100 = % Agreement