What Is Cronbach's Alpha? Reliability Thresholds and Interpretation
Daniel Ha · Seoul National University PhD StudentWhat Is Cronbach's Alpha?
Cronbach's alpha (α) expresses, on a scale from 0 to 1, how consistently respondents answer the several items intended to measure the same concept. It is the most widely reported reliability coefficient for survey scales.
How Do Reliability and Validity Differ?
Reliability asks whether you measure consistently, validity whether you measure what you intend to measure. High reliability can coexist with low validity, so both must be checked.
How Do You Interpret Cronbach's Alpha?
A higher value means greater consistency across items, and 0.7 or above is the conventional acceptance threshold.
| Alpha value | Interpretation |
|---|---|
| 0.9 and above | Very high |
| 0.8 to 0.9 | High |
| 0.7 to 0.8 | Acceptable |
| 0.6 to 0.7 | Low (caution) |
| Below 0.6 | Insufficient |
Somewhat lower values are sometimes tolerated in exploratory research or when a subscale has few items.
What If Alpha Is Too Low?
The scale may have too few items, or items with poor consistency may be mixed in. Check the "Cronbach's alpha if item deleted" column in SPSS and review items whose removal raises alpha substantially. Delete only where content validity is not compromised.
Is a Very High Alpha Also a Problem?
A value well above 0.95 can mean the items are effectively repeating the same content (item redundancy). In that case the scale fails to capture the concept broadly, so the item set should be reconsidered.
Summary
Cronbach's alpha indicates the internal consistency reliability of a scale, with 0.7 generally treated as the threshold. Review item deletion when it is low and redundancy when it is excessively high, and check structural validity alongside reliability with factor analysis.