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[Psychometric properties of a scale: internal consistency]
Adalberto Campo-Arias1, Heidi C Oviedo
1Instituto de Investigación del Comportamiento Humano, Bogotá, Colombia. campoarias@comportamientohumano.org
Revista De Salud Publica (Bogota, Colombia)
|April 11, 2009
Summary
Internal consistency reliability measures how well scale items correlate. Acceptable reliability ranges from 0.70 to 0.90, requiring 5-25 participants per item for accurate assessment.
Area of Science:
- Psychometrics
- Statistical analysis
Background:
- Internal consistency reliability assesses the interrelatedness of items within a measurement scale.
- It is a crucial aspect of scale validation in research.
Purpose of the Study:
- To define and explain internal consistency reliability.
- To outline methods for its calculation and acceptable ranges.
- To provide guidelines on sample size requirements.
Main Methods:
- Kuder-Richardson's formula 20 for dichotomous items.
- Cronbach's alpha for polytomous items.
- Reporting acceptable ranges (0.70-0.90) and sample size considerations (5-25 participants per item).
Main Results:
- Internal consistency is determined by item correlation.
- Specific formulas exist for dichotomous and polytomous data.
- Reliability varies by population, necessitating reporting.
Conclusions:
- Internal consistency is vital for scale validity.
- Appropriate calculation methods and reporting are essential.
- Reliability estimates should always be reported when using a scale.
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