How to Calculate IOA

by Leslie Renico; Updated September 26, 2017

Interobserver agreement (IOA) is one of the metrics used in measuring and analyzing behavior. Partial-interval recording measures whether or not certain behaviors occurred during particular time intervals, and in subjective areas, such as student discipline, several observers are needed to ensure that results are valid; for example, two different observers' idea of compliance in remaining seated might differ slightly. If the student moved up onto his knees briefly and then sat back down, different observers might record that event differently. IOA gives a mean reading to smooth out those areas of difference.

Step 1

Decide what behavior measures you will track during a given time period. Give each observer a recording sheet with instructions as to what to look for, and make sure that all observers use the same symbols to mark positive and negative correlations with expectations. For example, if a student is expected to raise her hand before speaking, mark times she does that -- but also mark times when she speaks out first.

Step 2

Have your observers count the total number of times the student talked in class and divide the number of correct behaviors by this number. This will give the percentage of intervals in which the student behaved correctly.

Step 3

Collect all the observation sheets and compare the markings. Count the total number of times the student spoke out in class.

Step 4

Count the number of times all observers rated the same behavior in the same way, either positively or negatively.

Step 5

Divide the answer from Step 4 by the answer in Step 3 and multiply by 100. This will give you the IOA, or intervals of agreement, in percentage form. For validity, this should be 80 percent or higher.