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Cronbach’s alpha & effect sizes
Is your scale reliable? How large is the effect?
Effect size from your values
What does it mean?
Alpha measures how strongly the items of a scale measure the same thing. Very high values (above 0.95) may indicate duplicate items. If alpha is low, check whether an item needs reverse coding.
Learn more
- Reliability and validityReliability means a measure gives consistent results; validity means it measures what it is meant to. A measure can be reliable without being valid.
- Likert scaleA Likert scale measures attitudes with several agreement items, usually rated from 1 (strongly disagree) to 5 or 7 (strongly agree), combined into one score.
- Inter-rater reliabilityInter-rater reliability shows how consistently two or more coders apply the same codes. Cohen’s kappa corrects for chance; κ above 0.60 is usually acceptable.
- Effect sizeAn effect size tells you how large a difference or relationship is, independent of sample size. Cohen’s d of 0.2, 0.5 and 0.8 is small, medium, large.
- Cronbach’s alphaCronbach’s alpha measures the internal consistency of a scale: how well its items measure the same construct. Values of .70 and above are acceptable.
- Reporting statistics in APAAPA style reports test statistic, degrees of freedom, exact p-value and effect size, e.g. t(13.46) = 3.42, p = .004, d = 1.71. Examples for every test.
