Mean duration, latency and IRT calculator
Enter several timed responses to get the total and the mean (average). The same arithmetic works for duration, latency and interresponse time; only what you timed is different.
How to calculate a mean
Mean = total of all the times ÷ number of times. Convert everything to the same unit first; seconds are easiest.
Example: four tantrums last 2:00, 1:30, 3:15 and 0:45. In seconds that's 120 + 90 + 195 + 45 = 450 seconds. 450 ÷ 4 = 112.5 seconds, a mean duration of 1 minute 52.5 seconds. The total duration, 7:30, is also worth reporting: it says how much of the session was lost to tantrums.
Duration, latency or IRT?
- Duration times each response from start to end: tantrums, time on task, crying.
- Latency times from a cue or instruction to the start of the response: how long it takes to start cleaning up after "Time to clean up".
- Interresponse time (IRT) times the gap between the end of one response and the start of the next: the time between bites of food or between hand raises.
All three are continuous measures and need a clear definition of when the response starts and ends.
Practice problems
| Problem | Answer |
|---|---|
| Three tantrums last 4, 6 and 8 minutes. Mean duration? | (4 + 6 + 8) ÷ 3 = 6 minutes. Total duration: 18 minutes. |
| After "Line up", a student starts walking after 10, 25 and 40 seconds. Mean latency? | (10 + 25 + 40) ÷ 3 = 25 seconds. |
| Gaps between bites at lunch are 30, 45, 20 and 25 seconds. Mean IRT? | 120 ÷ 4 = 30 seconds. |
| Crying lasts 1:30, 2:15 and 0:45. Mean duration? | 90 + 135 + 45 = 270 seconds; 270 ÷ 3 = 90 seconds (1:30). |
On the RBT exam
This calculator practises task A.6 Calculating and summarizing data. On the exam you get a dry-erase board but no calculator, so once you've checked a few answers here, practise doing them by hand.