To calculate mean count per interval IOA, divide the smaller count by the larger count within each matched interval, multiply by 100, then average the interval percentages. Preserve both observers' interval counts. Predefine how intervals with zero events for both observers are handled because many zero-zero intervals can raise the summary without testing occurrence agreement.

Align intervals exactly

Use the same interval boundaries, clock, pauses, and exposure for both observers.

Calculate every interval

Keep unrounded interval percentages until the final average. Preserve the underlying counts.

Declare the zero-zero rule

State whether joint-zero intervals enter as 100% and report how many occurred. Consider a method focused on occurrence when events are rare.

Inspect disagreement location

Averages can hide one poor interval. Review the intervals that matter to the clinical decision.

Preserve the interval ledger and averaging rule

Create one row per matched interval with both counts, the smaller value, the larger value, the unrounded fraction, and the validity state. Average the interval percentages with equal weight only when that is the declared method. The resulting mean gives each interval one vote, regardless of how many events occurred in it.

That weighting is part of the interpretation. A low-count interval can affect the mean as much as a high-count interval. If event volume matters to the decision, show total-count agreement or the underlying count differences beside the mean count-per-interval result instead of silently changing weights.

Test the effect of joint-zero intervals

When both observers record zero, the smaller-over-larger formula is undefined. Some implementations score that joint-zero interval as 100%, while others exclude it for this calculation and report it separately. State the rule before reviewing results, publish the number of joint-zero intervals, and show a sensitivity result when the choice materially changes the conclusion.

For rare events, many joint zeros can produce a strong mean even if the observers disagree whenever events occur. An occurrence-focused method can answer that narrower question. The report should also state how many planned intervals were matched, missed, invalid, or observed by only one person.

Use the formula and units for Jamal

For Jamal's mean count-per-interval IOA worksheet: mean count-per-interval IOA = sum of each interval's smaller count / larger count × 100 / intervals scored. Keep observer records independent until both are locked. Preserve the matched exposure, raw observations, numerator, denominator, unrounded calculation, and final rounding.

Work the arithmetic for Jamal

Jamal's interval counts are Observer A: 2, 1, 3, 1 and Observer B: 1, 1, 2, 1. Interval agreements are 50%, 100%, 66.7%, and 100%. Their mean is 316.7 / 4 = 79.2%. The interval records show where disagreement occurred.

The unrounded sum is 50 + 100 + 66.666... + 100 = 316.666..., and dividing by four gives 79.166..., displayed as 79.2%. The same records total 7 events for Observer A and 5 for Observer B, so total-count agreement is 5/7 = 71.4%. Exact counts match in two of four intervals, or 50%. These summaries differ because they ask different questions.

Apply interval count agreement to the decision

Jamal's qualified clinician identifies the decision before choosing an agreement method or threshold. Compare a stricter or complementary method when prevalence, totals, or aggregation could hide relevant disagreement. Repair definitions, visibility, training, sampling, or matching before judging the implementer or client data.

Audit observer and sample conditions for Jamal

Jamal's record identifies observers, independence, training, recording mode, shared exposure, response definition, procedure version, observation coverage, missing pairs, reactivity, and disagreements. Consent, privacy, recording, employment, supervision, and payer rules remain separate requirements. Keep every open pair visible with an owner and next action.

Protect client access during Jamal's observation

Jamal's observation keeps AAC, interpreters, mobility, food, water, bathroom use, prescribed care, health support, rest, relationships, and emergency help available. Do not create extra distress or remove ordinary supports to obtain an agreement sample. Record when access, health, withdrawal, or observer presence changes the condition.

Ask five IOA questions for Jamal

Use these questions in the mean count-per-interval IOA worksheet:

  • Did both observers independently score the same exposure, unit, definition, and condition?
  • Which calculation, numerator, denominator, prevalence, and rounding reproduce the result?
  • Which disagreements, missing pairs, invalid units, reactivity, or matching problems remain?
  • Which validity, treatment-integrity, client-outcome, experience, and access questions stay separate?
  • Which repair, complementary method, next sample, owner, and review date follow?

Keep raw observer records and disagreement types available.

Use current sources within their scope for Jamal

For Jamal's mean count-per-interval IOA worksheet, the BACB ethics hub points to current professional ethics materials. The CASP public summary provides high-level autism-treatment scope without licensed detailed procedures. The BACB Ethics Code addresses competence, client involvement, consent and assent when applicable, documentation, risk, supervision, and evaluation for covered behavior analysts. The BCBA Test Content Outline includes measurement, reliability, sampling, and data-based decisions as examination content rather than a case protocol.

For Jamal, Vollmer, Sloman, and St. Peter Pipkin discuss practical implications of data reliability and treatment-integrity monitoring. Essig, Rotta, and Poling review IOA and fidelity reporting in an identified ABA research corpus. Reed and Azulay describe a calculation tool and agreement methods. ASHA says AAC users should always have access to their tools or devices. These sources do not create one universal IOA method or threshold.

Close Jamal's agreement review

Ask Jamal and the responsible clinician to review the mean count-per-interval IOA worksheet through accessible communication. Record the method, arithmetic, sample, disagreements, limits, measurement repair, selected decision, next observation, and review date. Reopen the analysis when the definition, observer, system, exposure, prevalence, client access, procedure, or decision changes.

Clinician release checklist

  • Are interval boundaries, pauses, and validity states identical for both observers?
  • Can another reviewer reproduce all four unrounded interval fractions and the 79.2% mean?
  • Is the joint-zero rule declared even though this example has no zero-zero interval?
  • Are the 71.4% total-count and 50% exact-count views labeled as separate summaries?
  • Does the report show coverage, disagreement locations, limitations, and the next measurement action?

Related resources

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