Cronbach's alpha is a way of assessing reliability by comparing the amount of shared variance, or covariance, among the items making up an instrument to the amount of overall variance.

Cronbach's alpha is a way of assessing reliability by comparing the amount of shared variance, or covariance, among the items making up an instrument to the amount of overall variance. The idea is that if the instrument is reliable, there should be a great deal of covariance among the items relative to the variance.

1. Reliability of an instrument MURIEL N. CACERES, PhD Student CRONBACH’S ALPHA 1

2. Questions to consider.. 2 What is Cronbach’s alpha? How can I calculate it? How do I interpret the results? 2

3. 3 What is Cronbach’s alpha? Questions to consider.. 3

4. 4 What is Cronbach’s alpha? Is a measure of internal consistency reliability for a set of items or questions in a psychological test or survey. It assesses how consistently the items in a scale or test measure a single underlying construct. 4

5. What do I need Cronbach’s alpha for? You have formulated a hypothesis in which there is a variable that cannot be measured directly , so-called latent variable . In order to make the latent variables “measurable”, a scale is used. 5

6. What is a scale? Group of questions To measure a latent variable. 6

7. items goal The responses to the various items match well, i.e. are highly correlated. If the answers to the questions are highly correlated, this is called high internal consistency . CRONBACH’S ALPHA IS THE MEASURE OF THE INTERNAL CONSISTENCY OF A SCALE. 7

8. Thus, Cronbach’s alpha is a measure of the extent to which the group of questions are related. …and thus gives an estimate of how good or bad the measurement accuracy, the so-called reliability, of a group of items is. 8

9. Cronbach’s alpha does not test whether the individual items are really influenced by only one or by several latent variables. A high value of Cronbach’s alpha is not an evidence that the items are influenced by only one latent variable. ( Moosbrugger and Kelava 2012) 9

10. If all items measure the same latent variable… …then Cronbach’s alpha tells how well these items measure the latent variable. 10

11. for example… Your hypothesis: Extroverted people earn a higher salary than introverted people. How do I measure salary? What is your current net monthly income? _______________ But, how do I measure people’s extroversion? 11

12. Extraversion can be measured by a scale from the Big Five Personality Traits. Now, you can create a survey and calculate the Cronbach’s alpha. 12

13. Questions to consider.. 13 How can I calculate it? 1 3

14. How can I calculate Cronbach’s alpha? Number of Items One does not calculate Cronbach’s alpha by hand, but uses statistical software. Average inter-item covariance between items Average variance 14

15. Statistical softwares SPSS R MATLAB SAS STATA PHYTON EXCEL 15

16. Questions to consider.. 16 How do I interpret the results? 16

17. How DO I INTERPRET THE RESULTS? A general guide to interpreting Cronbach's alpha: Range of Values Interpretation Considering the Context Item Deletion Analysis Number of Items Comparison with Previous Studies Considering the Target Population Use in Conjunction with Other Validity Measures 17

18. Range of values Range of Values: Below 0.6: Generally considered low internal consistency. 0.6 to 0.7: Adequate internal consistency. 0.7 to 0.8: Good internal consistency. 0.8 and above: Excellent internal consistency. Cronbach's alpha ranges from 0 to 1, with higher values indicating greater internal consistency. 18

19. Cronbach's alpha interpretation from George and Mallery (2003). Values much larger than 0.9 are considered critical, as this indicates that some characteristics are too similar and thus the same thing comes out. 19

20. INTERPRETATION A low Cronbach's alpha may suggest that the items in the scale do not correlate well, and the scale may not be measuring a single underlying construct reliably. A high Cronbach's alpha indicates that the items are highly correlated, suggesting that they are measuring the same underlying construct consistently. 20

21. CONSIDER THE CONTEXT The acceptable range for Cronbach's alpha can vary depending on the context and the purpose of the measurement. Item Deletion Analysis If Cronbach's alpha is low, you may consider conducting an item deletion analysis. 21

22. Number of Items Scales with more items are likely to have higher alpha values, but a balance is needed to avoid redundancy and participant fatigue. Compare with Previous Studies Compare your Cronbach's alpha with similar studies or established scales in the literature to see how your measure compares. 22

23. Consider the Target Population The characteristics of the population being studied may influence the ideal level of internal consistency. Use in Conjunction with Other Validity Measures It's essential to consider other aspects of validity (e.g., content validity, construct validity) in conjunction with internal consistency to ensure the overall quality of the measurement. 23

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