Partial Interval Recording (PIR) is a discontinuous measurement method where you split an observation into equal time blocks and mark an interval “occurred” if the target behavior happens at any point during that interval. By the end of this guide, you’ll be able to choose PIR confidently, set up intervals that fit your setting, collect and score data accurately, calculate IOA, graph results, and streamline it all in Theralytics.
What Is Partial Interval Recording?
Layman's Term definition: In PIR you divide a session into intervals (e.g., 30 s). If the behavior occurs at least once in an interval, you score a “+”; if it does not occur at all, you score a “–”. You will then take the total amount of intervals behavior did occur and divide it by the total number of overall intervals. Report the outcome as % of intervals with occurrence.
Quick examples
- Classroom: “Talking out of turn” during 30‑s intervals. Any call‑out within an interval = “+”.
- Home: “Hand flapping” in 10‑s intervals. Any flap within an interval = “+”.
When practitioners use PIR: For high‑rate or brief behaviors, or when onsets/offsets are ambiguous and continuous recording isn’t feasible.
PIR vs Whole‑Interval vs Momentary Time Sampling (MTS)
One‑sentence examples
- Classroom: PIR for “calls out” every 30 s, mark “+” if behavior occurred at all; WIR for “on‑task for the entire 1 min interval”; MTS check if the student is “seated” every 2 min.
- Home: PIR for “shirt picking” in 15‑s intervals; WIR for “brushing teeth entire 30 s”; MTS glance at 1‑min marks for “playing independently.”
Pros, Cons, and Limitations (So You Pick the Right Method)
Pros
- Feasible during long sessions or with multiple learners.
- Sensitive to decreases in high‑rate behavior.
- Less continuous attention than event/duration recording.
Cons/limitations
- Overestimates relative to true duration/frequency (brief instance = full interval).
- Percent of intervals ≠ true rate or duration (construct validity caution).
- Choice of interval length meaningfully affects accuracy.
Choose another method when…
- You need exact counts → use frequency/rate.
- You need how long → use duration.
- Constant observation is impractical across many learners → consider MTS.
Step‑by‑Step: How to Run a Partial Interval Recording Session
1) Define the target behavior (observable, measurable)
Write clear, objective behavioral definitions (what counts / what doesn’t) to support training and IOA.
2) Set the observation window
Pick a realistic span (e.g., 15–30 min of typical instruction). Keep it consistent across sessions. Intervals should be influenced by gathering a baseline for the behavior to know how often it is occurring prior to data collection beginning. This will help you select the correct interval length.
3) Choose interval length
- High‑rate / brief behaviors: 10–30 s.
- Lower‑rate / longer behaviors: 1–5 min.
Shorter intervals → more accuracy but more effort, pick a cadence that matches the behavior and observer capacity.
4) Prepare your data sheet/timer (paper or app)
Use a printed PIR grid or a digital tool. Printable pattern: download a free interval‑recording sheet with “+ / –” boxes and % calculation prompts.
5) Observe and mark
At any time within an interval: behavior = “+”; no behavior = “–”. Stay with your rule; don’t count duration or frequency inside the block.
6) Tally & calculate
% intervals = (# of “+” intervals ÷ total intervals) × 100.
7) Graph & interpret
Graph % of intervals across sessions. Mark phase changes (baseline → intervention). Look for level, trend, and variability.
Worked Example (With Complete Sheet)
- Scenario: “Talking out of turn” during a 20‑minute class, 40 × 30‑second intervals. Below is the full interval grid for one session (8 rows × 5 intervals).
- Key: “+” = occurred; “–” = did not occur.
- Tally: 14 “+” out of 40 intervals
Calculation: (14 ÷ 40) × 100 = 35% of intervals with talking out of turn. - Second session (summary): 24 “+” out of 40 = 60%.
Trend: 60% → 35% (improved). Important: This reflects fewer intervals with any occurrence, not fewer total call‑outs per se.
Interobserver Agreement (IOA) for PIR
Why it matters: IOA verifies that two trained observers, using the same definitions and intervals, record the same events. High IOA supports data credibility and treatment decisions.
1) Interval‑by‑Interval (I×I) IOA
What it is: Agreements on both occurrence and nonoccurrence across all intervals.
Formula: (Agreements ÷ Total intervals) × 100.
Tiny example (10 intervals): 8 intervals matched → 80% I×I IOA.
2) Scored‑Interval IOA
What it is: Only considers intervals where at least one observer scored an occurrence (“+”).
Formula: (Agreements on “+” ÷ Intervals with ≥1 “+”) × 100.
Use when: Behavior is low‑rate, reduces the inflation from many “–” intervals.
Tiny example: Occurrence in 5 intervals total; both marked “+” in 3 → 60% scored‑interval IOA.
3) Unscored‑Interval IOA
What it is: Only considers intervals where at least one observer scored nonoccurrence (“–”).
Formula: (Agreements on “–” ÷ Intervals with ≥1 “–”) × 100.
Use when: Behavior is high‑rate, reduces chance agreement on frequent “+”.
Tiny example: Nonoccurrence in 7 intervals; both marked “–” in 5 → 71.4% unscored‑interval IOA.
Common Mistakes (and How to Fix Them)
Avoid common pitfalls when using partial interval recording (PIR) by ensuring your intervals are appropriately sized – overly long intervals can inflate overestimation, while excessively short ones can overwhelm staff; aim to match interval length to behavior tempo, recognizing that shorter intervals, though more accurate, require greater effort. Address vague definitions by writing clear, observable criteria and practicing with sample clips to eliminate ambiguity. Remember that PIR estimates the proportion of sampled intervals with any occurrence, not the frequency or duration of engagement. If interval sizes must be adjusted mid-phase, document the change and consider adding a new phase line. Finally, never skip observer training; always rehearse with agreement checks before live data collection.
Clinical Decision Rules & Troubleshooting
When deciding on a measurement method, if your percentage intervals consistently hover near 0-10% or 90-100%, PIR (Partial Interval Recording) loses sensitivity; at this point, adjust the interval length or switch to frequency/duration for precision or MTS (Momentary Time Sampling) for efficiency. If the behavior is briefer or faster than your block, shorten intervals; if observers are overloaded, lengthen them slightly, always expecting trade-offs between accuracy and effort. For clinical decisions, many single-case standards suggest interpreting trends only after collecting at least 3-5 data points per phase, though more is always better when feasible, and any exceptions should be documented. When dealing with very high-rate behaviors, consider using unscored-interval IOA and potentially MTS if continuous observation is impractical, while for very low-rate behaviors, scored-interval IOA or frequency recording might be more appropriate.
Templates & Tools
For quick paper workflows, printable PIR data sheets with “+ / –” boxes and built‑in % calculations are available from reputable teaching resources. Alternatively, Theralytics supports a digital workflow, allowing for interval recording, real‑time data entry, and interactive graphs that automatically aggregate % intervals and trends. Its mobile app works offline on iOS/Android for field sessions and maintains HIPAA compliance. Theralytics’ discontinuous‑measurement guide also offers pragmatic interval choices (e.g., 10–30 s for high‑rate; 1–5 min for lower‑rate) and includes automated interval prompts, reminders, and graphs to help reduce human error.
Reporting, Graphing, and Explaining PIR Data to Stakeholders
Graphing:
- X‑axis: date/session.
- Y‑axis: % of intervals with behavior.
- Add clear phase change lines (Baseline, Intervention A/B).
Labeling: Include target name, interval length, observation window, setting, and who collected the data.
Today, talking out of turn happened in 35% of sampled time blocks, down from 60% last week. That means fewer intervals with any calling out. We’ll keep the same support and check again next session.
Evidence & Further Reading (Practitioner Takeaways)
- Bias patterns: PIR tends to overestimate duration, while MTS may over‑ or underestimate depending on parameters, often aligning more closely with duration than PIR; nonetheless, both methods can lead to similar treatment conclusions in practice. Choose based on your goal and context.
- Efficiency vs accuracy: Interval methods trade precision for feasibility; shorter intervals increase accuracy but require more work.
- Momentary sampling & multitasking: MTS allows periodic checks without continuous observation, useful in classrooms or groups.
Collecting Partial Interval Recording Data in Theralytics (Quick Workflow)
- Create the target in Theralytics and select Interval Recording as the measurement type.
- Set interval length (e.g., 30 s) and observation window (e.g., 20 min).
- Start session on the Mobile App (works offline).
- Use the app’s interval prompts/reminders; at each interval, tap “occurred / not occurred” for the target(s).
- End session → % intervals and a graph are created automatically; view, filter, and share.
- Export/report with HIPAA‑compliant safeguards and auditability.
Conclusion
PIR is designed to sample behavior efficiently by marking whether it happened at any point in each interval. Use it for high‑rate/brief targets when continuous measurement is impractical, and interpret the result as % of intervals, not true rate or duration. Clear definitions, right‑sized intervals, and solid IOA keep your data trustworthy. Theralytics streamlines the entire process, from interval timing and quick taps to automatic graphs and reporting, so teams can focus on intervention, not paperwork.
Frequently Asked Questions (FAQs)
Does PIR measure severity or duration?
No. PIR reflects presence within intervals, not how intense or how long the behavior lasted. Use duration or frequency if you need those.
What interval length should I choose?
Match the behavior’s cadence and observer feasibility. Start short (10–30 s) for high‑rate behaviors; 1–5 min works for lower‑rate or longer behaviors. Shorter = more accurate, more effort.
Why do my PIR results seem “inflated”?
Overestimation is expected because any brief instance fills the whole interval; that’s one reason PIR is often used for decreasing behavior.
How do I calculate IOA for PIR?
Common options: I×I IOA, scored‑interval, and unscored‑interval. Example (scored‑interval): if both observers agreed on occurrence in 3 of the 5 intervals with any “+”, IOA = 3/5 = 60%. Use scored for low‑rate, unscored for high‑rate.
When should I use MTS instead?
If constant observation is impractical (e.g., supervising multiple learners), MTS lets you look up at specific moments and still capture meaningful trends.
Can I do PIR while supervising multiple learners?
Yes, use interval prompts/reminders and simple taps in software to stay on schedule and reduce errors.
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