Dana Do’s: Why IOA Math Should Not Intimidate You

Don’t be afraid of IOAs, that’s Interobserver Agreement. I always hear students say, “I hate math, so I’m not good at IOA”. As someone who doesn’t enjoy math, I can tell you that IOA math should not intimidate you. What is intimidating, however, is the number of formulas we need to know. To be precise, there are nine IOA formulas. While they are easy math formulas, they can be hard to memorize. They also vary, slightly. But as per usual, I have some tips to make it less scary.

• First of all, connect the formulas by the type of data that’s being agreed upon. If the measurement is count, rate, or frequency, then you want to utilize one of the three count IOAs: total, mean, or exact count.
• If the measurement being compared is duration, which would also include IRT and latency, then you’ll want to choose one of the two duration IOAs: total or mean duration.
• If the observers are comparing trial-based data (for example: correct versus incorrect responses, DTT, think percentage of opportunity measures), then you will want to use trial-by-trial IOA.
• If you are looking at two observers’ time sampling measures, then you are dealing with agreements about the occurrence or non-occurrence of behavior. In these cases, you want to use scored, unscored, or interval-by-interval IOA.

This trick should, at minimum, help you narrow some things down in your exam questions.

A great tip to know is that some of the interobserver agreement formulas use the same math, so connecting those formulas should lessen the study load a little. For example:

• Total count and total duration formulas use exactly the same math. The difference is just that what is being compared is different.
• Count versus duration, mean count and mean duration also the same math formula. But again, what is being compared is different: count versus duration.
• Finally, trial-by-trial and interval-by-interval have the exact same math formula but what is being compared is the correct and incorrect responses, versus occurrence and non-occurrence of behavior.

While there’s obviously a lot more to know when it comes to the interobserver agreement formulas, these simple tips can help you narrow your discrimination.

For 30 IOA practice opportunities, download the free PTB IOA Mini Manual.

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Reactivity

Refers to the changes in an individual’s behavior due to the presence of an observer.

Measurement bias

When an observer’s measurement is influenced by an expectation or belief they hold rather than what actually occurred.

Observer reactivity

When an observer’s data collection or performance is influenced by the awareness that they are being monitored and evaluated.

Interobserver agreement (IOA)

A measurement of the degree to which two or more observers report the same values when observing and collecting data for the same behaviors/events.

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Measurement is trustworthy when the measurement that produces data is applicable and specific to the target behavior of interest and the relevant dimension of that behavior; in other words, you …

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Reliability

Measurement is trustworthy when the degree to which repeating a measurement procedure under the same conditions produces the same result.

Measurement artifact

Data that represents an unwarranted and misleading picture of behavior because of how it was measured, typically a product of time-sampling, limiting measurement scales, or poorly scheduled measurement periods.

Observer drift

When observers collecting data have a shift/drift in how they interpret the operational definition of the target behavior that affects the validity of their data.

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