Likert scale used to asses attitude or opinion of participants. Reliability of such a scale is assessed by Cronbach's alpha test.
Now to create a knowledge score on vaccine preventable diseases. Each participants will be asked to identify the vaccine preventable diseases from 8 selected diseases. The response would be yes or no (two way close ended) . One score for correct answer and zero for wrong answer. Therefore there will be scale measuring knowledge in a range 0 to 8. The higher the number the higher the knowledge.
Any way to test reliabilty of such knowledge scales like Likert scale?
hello,
the following article might be of help as it s about Selecting, designing, and developing your questionnaire.
http://discovery.ucl.ac.uk/1980/1/1312.pdf
Internal consistency with dichotomous items is a tricky thing. I have attached a couple of articles I use when teaching psychometrics that are useful in laying out the problems (Sitjtsma) and some alternatives (Trizano-Hermosilla & Alvarado).
Let me ask you a question. (I'm interested in this, since I'm doing something similar re knowledge about Zika in the US). Am I correct in that the questions are:
1) Can pneumonia be prevented by vaccination? y / n
2) Can acne be prevented by vaccination? y / n
3) Can rubella be prevented by vaccination? y / n
4) Can polio be prevented by vaccination? y/n
5) Can Marburg be prevented by vaccination? y/n
If so, then just summing the responses is not correct -- presumably everyone knows acne can not be prevented, and many would have been vaccinated for polio; but only some would know about pneumonia, and few would even know of the existence of Marburg. The proper approach, I would argue, is a confirmatory factor analysis approach using tetrachoric correlations between the items, as suggested by, say, Glockner-Rist, Angelika, and Herbert Hoijtink. "The best of both worlds: Factor analysis of dichotomous data using item response theory and structural equation modeling." Structural Equation Modeling 10, no. 4 (2003): 544-565. Happily, that article is available online. Most statistical packages can do the necessary computations.
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