Meaning of Cronbach's alpha
Cronbach's Alpha is a coefficient that is used to measure the reliability of a measurement scale, and whose name Alpha was made by Cronbach in 1951.
The alpha Cronbach is an average of the correlations between the variables that are part of the scale. It can be calculated in two ways: from the variances (Cronbach's alpha) or from the correlations of the items (standardized Cronbach's alpha) .
The alpha coefficient can be used as an index of internal robustness . But it does not imply anything about stability in time or about the equivalence between alternate forms of the instrument.
- The alpha coefficient can be displayed as the lower limit of the reliability coefficient known as the precision coefficient. In other words, an alpha coefficient of 0.80 only implies that the precision coefficient is greater than 0.80, but it is not known by how much it differs.
- The alpha coefficient can be visualized as the average of all the reliability coefficients obtained by the two-half methods.
- The alpha coefficient is not an index of one-dimensionality of the instrument.
- The alpha coefficient can be used in any situation in which you want to estimate the reliability of a compound.
There are factors that can affect reliability, such as:
- Homogeneity of the group.
- Weather.
- Size of the questionnaire .
- Objectivity of the process of assigning scores.