If you a marketing or management student (Bachelor, Masters or PhD) or professional wishing to measure consumer or participant’s perceptions, you should use the marketing handbook of scales.
In this previous article I explained how the handbook works and how the scales are structured. And after you have used them, there is something very important to calculate: its RELIABILITY.
Cronbach alpha is the most common and adopted test to measure the internal consistency of a scale. In other words, it will give you an indication of how closely related the items are in measuring a particular factor. Also important to remember:
- It does not apply for single items (the scale must have 3 or more items)
- Results from Cronbach alpha tests range from 0.0-1.0
- How to interpret results? Well, according to Field (2016), reliability scores:
- Under .6 are considered “unacceptable”.
- Above .6 are considered “questionable” (some authors accept it, some do not).
- Scores above .7 are considered “acceptable” is most social sciences.
- Scores above .8 represent that your scale has achieved a “good” reliability level.
- Scores above .9 represent that your scale has achieved an “excellent” reliability level.
Here is a quick SPSS Tutorial on how to conduct and interpret the test:
So these are the basics regarding Cronbach alpha reliability tests and how to conduct them on SPSS. In case you would like to know more in-depth, here are some additional sources I would suggest:
- Coefficient Alpha and the Internal Structure of Tests (Original paper from Lee J. Cronbach, in 1951)
- Cronbach’s Alpha: A Tool for Assessing the Reliability of Scales (Santos, 1999)
- Making Sense of Cronbach’s Alpha (Tavakol and Dennick, 2011)
One final important reminder:
- In case you reliability score has been under .6 (therefore considered “unacceptable”), please report it anyway. It is very important for the reader to be aware of it when interpreting your results.
- And you can even remind the reader to interpret that particular result “with care”, as the scale had not reached the expected reliability score, ok?
So all the best, drink lots of coffee, go running three times a week and enjoy the start of the new 2018/2019 football season!