IOC Calculator
Paste your experts' ratings and see right away which items to keep and which to revise.
1 Paste the expert ratings
1 row = 1 item · each column = 1 expert (rating +1, 0 or −1) · an item label in the first column is optional
Decision rule
- IOC ≥ 0.50 → keep the item
- IOC < 0.50 → revise or remove
IOC per item
| Item | ΣR | N | IOC | Decision |
|---|---|---|---|---|
| Q1 | 2 | 3 | 0.67 | Keep |
| Q2 | 3 | 3 | 1.00 | Keep |
| Q3 | 0 | 3 | 0.00 | Revise / remove |
| Q4 | 2 | 3 | 0.67 | Keep |
Text for your report (Chapter 3)
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What is the IOC?
The Index of Item-Objective Congruence (IOC) is a way to check the content validity of a questionnaire or test: whether each item really measures the objective or construct it was written for. Content experts rate every item +1 (clearly congruent), 0 (unsure) or −1 (clearly not congruent).
It is widely used in Thai theses and research reports as the step between drafting the questionnaire and running a try-out for reliability.
Formula
IOC = ΣR / N
- ΣR — sum of all experts' ratings for the item
- N — number of experts
Example: three experts rate an item +1, +1 and 0, so IOC = (1 + 1 + 0) / 3 = 0.67. That is at least 0.50, so the item is kept.
Keep the item.
Revise it using the experts' comments, or remove it.
After IOC: reliability
Once the items pass, try the questionnaire out with a small group and compute Cronbach's alpha to show the scales are reliable. IOC answers "does each item measure the right thing?"; alpha answers "do the items measure it consistently?".
Reference: Rovinelli, R. J., & Hambleton, R. K. (1977). On the use of content specialists in the assessment of criterion-referenced test item validity. Dutch Journal of Educational Research, 2, 49–60.
Frequently asked questions
What IOC value is acceptable?
Items with an IOC of 0.50 or higher are treated as content-valid and kept. Items below 0.50 should be revised following the experts' comments, or removed.
How is the IOC calculated?
IOC = ΣR / N, where ΣR is the sum of the experts' ratings for one item (each expert gives +1 congruent, 0 unsure, or −1 not congruent) and N is the number of experts.
How many experts do I need for IOC?
An odd number of experts, usually 3 or 5, is common so that ratings do not split evenly. Each expert rates every item +1, 0 or −1 against the objective or construct it is meant to measure.
How is IOC different from Cronbach's alpha?
IOC checks content validity: whether each item measures what it is supposed to, judged by experts before data collection. Cronbach's alpha checks reliability: whether the items of a scale answer consistently, computed from try-out responses. Most theses report IOC first, then alpha.
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