Cronbach's alpha estimates how consistently a set of items measures the same construct. Targets, formula and when it misleads.
Cronbach's alpha estimates internal consistency: how much the items in a scale hang together as one measure. It ranges 0-1; .70 is the accepted floor for new scales, .80-.90 is comfortable for production surveys.
α = (k/(k−1)) × (1 − Σσ²ᵢ / σ²total) — k items, item variances vs total variance.
Six confidence items on a leadership survey produce α = .84: they behave like one construct, so averaging them into a single score is justified.
Report it whenever you average several items into one score—it tells readers the average is measuring something stable.
Alpha inflates with more items and deflates with heterogeneous dimensions; a low alpha often means your scale has two constructs, not a broken scale.
≥.70 for a new instrument, ≥.80 for scales you will report to clients. Above .95 usually means duplicate items—trim them.
No—alpha applies to multi-item scales only. One standalone question has no internal consistency to test.
Turn the concept into a live assessment：Cronbach's Alpha
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