Interval-by-interval IOA is a straightforward way to measure IOA. Both observers record the occurrence or non-occurrence of the behavior of interest. No frequency or duration are recorded. Percentage agreement is then calculated using the number of intervals in which the observers agreed by the total number of intervals. See the example below.
X- Occurrence O- Non-occurrence
The observers agreed during intervals 2, 3, and 5 (three intervals with agreement).
Five total intervals were recorded.
3/5 *100= 60% agreement