Standardized alpha: what it means and how to read it

In the report: Alpha standardized — Alpha from the mean correlation of the items, as SPSS "Based on Standardized Items": as if every item had the same variance.

How to read it

It differs from alpha when the items have very different spreads; report it when the items are on different scales.

In plain words

A teacher's quiz had some questions answered from 1 to 5 and others from 1 to 10. She worried that the questions with more answer choices would count for more than the short ones. The usual alpha said that about 78 parts of 100 of the differences between students come from the one thing all the questions catch. She also looked at the standardized alpha, which gives every question the same weight. It came out 0.84, about 84 parts of 100. Now she knows the questions hang together a bit better than the first number said. Since her questions use different ranges of answers, the standardized alpha is the one she reports.

How it is computed

k · r̄ / (1 + (k − 1) · r̄), r̄ — the mean correlation between the items

Example

The cell with Alpha standardized is selected in each report; point at a label to see its note.

— the sample data (50 rows) the examples use
— Standardized alpha next to alpha, and in the if item deleted table =STATS_ALPHA(Data!A1:T51, "/^q/", TRUE, "", TRUE)

Where you see it

STATS_ALPHA — Computes Cronbach’s Alpha — a measure of internal consistency (reliability) for a set of items, such as Likert-type questions.

Alpha if the item is deleted — The alpha (or the standardized alpha) of the remaining items without this one.
Corrected item-total correlation — The correlation of the item with the sum of the other items (the item itself left out of the sum), as SPSS RELIABILITY "Corrected Item-Total Correlation". Empty for an item without spread.
Cronbach’s alpha — Cronbach’s alpha: how consistently the items measure the same thing, on the rows where every item is answered.

Get it in your sheet

One formula in a cell gives the whole report, Standardized alpha included. ALS Stats is a free add-on for Google Sheets™.

Install ALS Stats from Google Workspace Marketplace (opens in a new tab)