Total Count IOA
Formula: (Smaller Total / Larger Total) x 100. Example: Observer A records 18 responses; Observer B records 20 responses. IOA = (18/20) x 100 = 90%. Limitation: Can inflate agreement if both observers record the same total but during different instances. Best for: Quick check when behavior occurs at moderate rates.
Exact Agreement (Interval-by-Interval) IOA
Formula: (Number of Intervals with Agreement / Total Number of Intervals) x 100. Example: Out of 20 intervals, both observers agree on 17. IOA = (17/20) x 100 = 85%. Agreements: Both scored occurrence OR both scored non-occurrence. Best for: Interval recording data where exact timing matters.
Trial-by-Trial IOA
Formula: (Number of Trials with Agreement / Total Number of Trials) x 100. Example: Out of 10 discrete trials, observers agree on 9. IOA = (9/10) x 100 = 90%. Best for: Discrete trial data or trial-based measurement.
Scored-Interval IOA (Occurrence Only)
Formula: (Agreements on Occurrence / Agreements on Occurrence + Disagreements) x 100. Use when: The behavior occurs at low rates and you want to ensure agreement on when it did occur (not just that it did not occur). More conservative than exact agreement IOA for low-rate behaviors.
Unscored-Interval IOA (Non-Occurrence Only)
Formula: (Agreements on Non-Occurrence / Agreements on Non-Occurrence + Disagreements) x 100. Use when: The behavior occurs at high rates and you want to ensure agreement on when it did not occur.
Acceptable IOA Thresholds
Generally, 80% or higher is considered acceptable for research and clinical practice. For high-stakes decisions or publication, 90% or higher is preferred. IOA should be calculated for at least 20-33% of sessions.