How to Calculate the Expected Proportion Correct for Each Ability Level
Calculating the expected proportion correct for each ability level is crucial in psychometrics and educational testing. It helps in predicting an examinee’s performance based on their ability level and the number of trials or items they attempt.
- Select the ability level from the dropdown menu.
- Enter the number of trials or items.
- Click the ‘Calculate’ button.
The formula to calculate the expected proportion correct is:
E(p) = a + (1 – a) * (1 – e^(-b * n))
Where:
- E(p) is the expected proportion correct
- a is the ability level (0.2, 0.5, or 0.8)
- b is a constant (0.147)
- n is the number of trials or items
| Ability Level | Number of Trials | Expected Proportion Correct |
|---|
- Understand that the expected proportion correct is a prediction and actual performance may vary.
- Use this calculator to set realistic goals and expectations for examinees.
- Consider using this information to inform test design and item selection.
What is an ability level?
An ability level is a measure of an examinee’s proficiency or skill in a particular domain or subject area.