To calculate interval by interval IOA, count matched intervals in which both observers agree on occurrence or both agree on nonoccurrence, divide by all intervals compared, and multiply by 100. Report occurrence prevalence and the agreement table. When behavior is rare, many joint-nonoccurrence intervals can produce a strong overall result despite weak occurrence agreement.

Align interval boundaries

Use the same timer, start, stop, pauses, interval length, and valid exposure.

Build a two-by-two table

Count both-occurrence, both-nonoccurrence, A-only occurrence, and B-only occurrence intervals.

Inspect prevalence

Report intervals with occurrence for either observer. Rare events can make joint absence dominate.

Add a conditional method when useful

Scored-interval agreement can focus on occurrence, while unscored-interval agreement can focus on nonoccurrence.

Reconcile the two-by-two table

Build four mutually exclusive cells: both observers record occurrence, both record nonoccurrence, Observer A only records occurrence, and Observer B only records occurrence. Their sum must equal the matched valid interval denominator. Keep intervals missed by either observer in a separate coverage table.

For Mira, the twelve intervals reconcile as two joint-occurrence agreements, seven joint-nonoccurrence agreements, and three disagreements distributed across the two one-observer cells. Nine agreement cells divided by twelve matched intervals produces 75%. The table reveals that most agreement comes from shared nonoccurrence.

Add occurrence and nonoccurrence views carefully

With the same binary table, scored-interval agreement is joint occurrence divided by intervals in which either observer recorded occurrence. Mira's scored-interval result is 2/(2+3) = 40%. Unscored-interval agreement is joint nonoccurrence divided by intervals in which either observer recorded nonoccurrence, giving 7/(7+3) = 70%.

Those percentages do not replace the overall result. They show where agreement is stronger and help a reviewer decide whether the measurement problem concerns detecting events or agreeing on their absence. Preserve the directional split of the three disagreements so observer-specific visibility or definition patterns remain detectable.

Use the formula and units for Mira

For Mira's interval-by-interval IOA worksheet: interval-by-interval IOA = intervals with matching occurrence or nonoccurrence scores / matched intervals compared × 100. 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 Mira

Mira's observers compare twelve intervals and agree in nine. Interval-by-interval IOA is 9 / 12 × 100 = 75%. Seven agreements are joint nonoccurrence and two are joint occurrence, so the method gives important prevalence context that the 75% alone omits.

Occurrence appears in five intervals for at least one observer, while nonoccurrence appears in ten intervals for at least one observer. These denominators overlap by design because each disagreement contains one occurrence and one nonoccurrence score. Label them clearly so readers do not try to add the conditional denominators.

Apply overall interval agreement to the decision

Mira'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 Mira

Mira'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 Mira's observation

Mira'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 Mira

Use these questions in the interval-by-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 Mira

For Mira's interval-by-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 Mira, 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 Mira's agreement review

Ask Mira and the responsible clinician to review the interval-by-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

  • Do the four table cells sum to all twelve matched valid intervals?
  • Can another reviewer reproduce overall agreement 9/12 = 75%?
  • Are seven joint nonoccurrences, two joint occurrences, and three disagreements visible?
  • Are scored-interval 2/5 = 40% and unscored-interval 7/10 = 70% labeled as conditional views?
  • Are coverage, interval length, prevalence, observer independence, and the next measurement repair documented?

Related resources

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