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Cronbach's alpha measures internal consistency: how far a set of items behave as though measuring one construct. It rises with both the number of items and their average intercorrelation.
Cronbach's alpha
α = (k/(k−1))·(1 − Σσ²ᵢ / σ²_total)
α = (5/4)(1 − 6/18) = 0.8333, which counts as good internal consistency.
Yes. Above about 0.95 the items are likely redundant, measuring the same narrow thing rather than the broader construct.