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psych.test-reliability-coefficient Calculator
Calculates Cronbach's alpha internal consistency coefficient from item-total correlations, indicating how well a test or survey scale measures a single construct. Alpha above 0.7 is acceptable for research; above 0.9 is excellent — below 0.6 suggests items measure different things.
Inputs
Test Variance
The square of standard deviation. Less intuitive than SD (units are squared), but used in many statistical formulas.
Sum Item Variances
The square of standard deviation. Less intuitive than SD (units are squared), but used in many statistical formulas.
Num Items
Count of items or occurrences.
Results
Cronbach alpha
pH of the solution. Below 7: acidic. 7: neutral. Above 7: basic (alkaline).
reliability interpretation
Qualitative summary of what the computed numbers mean in practical terms.
standard error of measurement
The difference between the computed result and the exact or true value — a measure of approximation accuracy.
Spearman-Brown prophecy (2×)
pH of the solution. Below 7: acidic. 7: neutral. Above 7: basic (alkaline).
research minimum alpha
The smallest value in the dataset or feasible range.
clinical minimum alpha
The smallest value in the dataset or feasible range.