Enter the number of items or tests, the sum of the variances of each item or test, and the total variance of the test scores into the calculator to determine the Reliability Coefficient.

## Reliability Coefficient Formula

The following formula is used to calculate the Reliability Coefficient.

RC = (k / (k - 1)) * (1 - (Σσ² / σt²))

Variables:

- RC is the Reliability Coefficient
- k is the number of items or tests
- Σσ² is the sum of the variances of each item or test
- σt² is the total variance of the test scores

To calculate the Reliability Coefficient, first calculate the sum of the variances of each item or test. Then, calculate the total variance of the test scores. Subtract the sum of the variances from 1. Multiply the result by the number of items or tests divided by the number of items or tests minus 1. The result is the Reliability Coefficient.

## What is a Reliability Coefficient?

A Reliability Coefficient is a statistical measure that indicates the consistency or stability of a set of measurements or testing scores. It ranges from 0 to 1, where a higher value indicates a more reliable or consistent set of data. This coefficient is often used in psychometrics to evaluate the reliability of psychometric instruments like questionnaires or tests. It helps to determine whether the instrument is measuring the concept consistently and accurately.

## How to Calculate Reliability Coefficient?

The following steps outline how to calculate the Reliability Coefficient.

- First, determine the number of items or tests (k).
- Next, calculate the sum of the variances of each item or test (Σσ²).
- Next, determine the total variance of the test scores (σt²).
- Next, use the formula RC = (k / (k – 1)) * (1 – (Σσ² / σt²)).
- Finally, calculate the Reliability Coefficient.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

Number of items or tests (k) = 5

Sum of the variances of each item or test (Σσ²) = 10

Total variance of the test scores (σt²) = 3