Need to Check Test Consistency? Try Guttman Lambda-6!

Welcome to the Guttman's Lambda-6 Calculator! Follow the steps below to calculate the Lambda-6 for your data.

  1. Download the example file: Click here to download an example file and follow these steps to prepare your data:
    1. Open your original dataset in Excel.
    2. Ensure that each item/response is in its own column, and each participant's responses are in a separate row.
    3. Save your file as a CSV (Comma delimited) (*.csv).
    4. Open the saved CSV file in Notepad to copy the comma-separated values.
  2. Paste Your Data: After copying your comma-separated values, paste them into the textarea below.
  3. Generate Table: Click the "Generate Table" button to view your data in tabular form.
  4. Calculate Lambda-6: After generating the table, click the "Calculate Lambda-6" button to get the result.

Guttman's Lambda-6 Formula

Guttman's Lambda-6 is a statistical measure used to assess the internal consistency of assessments with dichotomous choices (Guttman, 1945), similar to  Kuder-Richardson-20 (KR-20). However, while KR-20 assumes equal item variance, Lambda-6 does not, potentially providing a more accurate measure of reliability.

Internal consistency refers to the extent to which all the items in a test measure the same construct or trait. A higher internal consistency indicates that the items are well correlated with each other, suggesting that they are all measuring the same underlying characteristic.

The Guttman's Lambda-6 formula is expressed as:

\[ \lambda_6 = \frac{K(K-1)}{\sigma^2_X + (K-1)\bar{P}\bar{Q}} \]


The formula essentially adjusts the KR-20 formula to account for varying item variances, providing potentially more accurate results.


Guttman, L. (1945). A Basis for Analyzing Test-Retest Reliability. Psychometrika, 10(4), 255–282.

Nunnally, J. C. (1978). Psychometric theory (2nd ed.). McGraw‐Hill.

Publication: 2023