Scored interval IOA is typically used for low-rate behavior, and unscored interval IOA is generally used for high-rate behavior. Both use only a subset of data when IOA is calculated. Scored interval IOA only calculates the intervals in which one or both observers record an occurrence of the target behavior. Conversely, unscored interval IOA only calculates the intervals in which one or both observers record no occurrence of the target behavior. See the example below:
X- Occurrence O- Non-occurrence
Scored Interval IOA:
At least one observer recorded an occurrence during intervals 1, 2, and 4 (three intervals).
The observers agreed during interval 2, but not the intervals 1 and 4 (1 interval with agreement)
1/3 *100= 3% agreement
Unscored Interval IOA:
At least one observer recorded no occurrence during intervals 1, 3, 4, and 5 (four intervals).
The observers agreed during intervals 3 and 5, but not the intervals 1 and 4 (2 intervals with agreement)
2/4 *100= 50% agreement