KR-20 (Kuder–Richardson Formula 20) is an index of the internal consistency reliability of a measurement instrument, such as a test, questionnaire, or inventory. […].Values of KR-20 generally range from 0.0 to 1.0, with higher values representing a more internally consistent instrument. In very rare cases, typically with very small samples, values less than 0.0 can occur, which indicates an extremely unreliable measurement. A rule-of-thumb commonly applied in practice is that 0.7 is an acceptable value or 0.8 for longer tests of 50 items or more.
EXAMPLE OF USE
Subscales and total scores were compared by licensed and unlicensed programs using t-tests. To establish reliability for subscale and total scores, Cronbach’s alpha and Kuder-Richardson Formula 20 were conducted. Kuder-Richardson Formula 20 (KR-20) is an extension of the Cronbach’s alpha when the measures includes dichotomous items. The reliability coefficients were calculated in non-infant/toddler items (16–58) reported on <75% of settings. For infant/toddler items (59–87) reliability statistics were reported if >50% of settings were rated (Alkon and Cole, 2012: 557).