Calculating the reliability of a questionnaire or scale using SPSS: Cronbach's alpha coefficient

The development and application of measurement instruments is a common undertaking in socio-educational research. Questionnaires, scales and tests must be shown to be valid and reliable. Reliability, understood as the accuracy of the measurement of a characteristic or an attribute, can be calculated in several ways. Cronbach's alpha coefficient is one of the most frequently applied methods, and can be used in scale variables. The purpose of this article is to provide a general description of the functioning of Cronbach’s alpha and the operating procedure used to obtain it. The statistical program SPSS calculates this value relatively easily, helping to guide decisions regarding the use of a questionnaire or a test, since the significance of the coefficient takes into account the context in which it is applied. The objectives of the study are to identify the different methods to calculate the reliability of an instrument in the socio-educational field; to present the steps to calculate Cronbach's alpha using the SPSS statistical package; and to exemplify the calculation of the reliability of a Likert-type attitude scale.