Math
Standard deviation
Calculate population mean, variance and standard deviation for five values.
Calculators / Math / Cronbach alpha from variances
Cronbach alpha from variances calculator
Estimate internal consistency from the item count and observed item and total-score variances.
On this page
Cronbach alpha0.89
Calculator controls
How to calculate
Estimate internal consistency from the item count and observed item and total-score variances.
Cronbach alpha =
k/(k-1)*(1-sum/total)Worked example
- Number of scale items: 10
- Sum of item variances: 10
- Variance of total scores: 50
- Cronbach alpha: 0.89
Assumptions and limits
Variance summaries must come from the same respondents and scoring scheme. Alpha can be negative; it does not prove validity or unidimensionality.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate internal consistency from the item count and observed item and total-score variances. Do not sum standard deviations in place of variances. Reverse-scored items must be processed before computing these inputs.
When this tool is useful
Do not sum standard deviations in place of variances. Reverse-scored items must be processed before computing these inputs.
Understanding your inputs
| Input | Example |
|---|---|
Number of scale items k | 10 |
Sum of item variances sum | 10 |
Variance of total scores total | 50 |
Frequently asked questions
Which assumptions matter for this result?
Variance summaries must come from the same respondents and scoring scheme. Alpha can be negative; it does not prove validity or unidimensionality.
How can I check the worked example?
Use the displayed example inputs in the stated formula. Keep each quantity in its labelled unit and compare the unrounded result before applying display rounding.