I am designing a questionnaire by using five-point Likert scale. What is the advantage of five-point Likert scale over seven-point Likert scale?
Thank you.
Solved – Five-point or seven-point Likert scale
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Many psychological tests convert numeric raw scores into categories. For example, Wikipedia mentions cut-offs for the Beck Depression Inventory:
- 0–9: indicates minimal depression
- 10–18: indicates mild depression
- 19–29: indicates moderate depression
- 30–63: indicates severe depression.
Or for example the BMI define various cut-offs (e.g., Cole et al, 2007).
In general, you lose information by collapsing categories or using cut-offs. Psychological reality tends to be more continuous. That said, categories do have heuristic value as decision aides.
A few options for converting scores to a collapsed set of categories
- Use the logical definition of the scale points: For example, you might use "strongly agree" as highly productive, "agree" as productive, and the other categories as "not productive". This is a simple approach that uses the scale anchor points to define the meaning of the categories.
- Use expert judgements: You can ask a set of experts to evaluate where they thinlk the cut-offs between categories should be. These can then be synthesised. This approach is often used to define acceptable standards for various tests.
- Use normative information: You could use information about the normative spread of the variable and an assumption about the prevalence of the phenomena to define cut-offs.
- Use prediction of external criterion: If the thing has objective existence, or if there are things related to it, you could use predictive models of this external criterion to define the categories.
References
- Cole, T. J., Flegal, K. M., Nicholls, D., & Jackson, A. A. (2007). Body mass index cut offs to define thinness in children and adolescents: international survey. Bmj, 335(7612), 194. FULL TEXT
There should be other considerations on your Likert scales than just the number of categories.
Do you offer a neutral category? Compare: "Strongly disagree - Disagree - Agree - Strongly Agree" vs. "Strongly disagree - Disagree - No opinion - Agree - Strongly Agree". The first scale has a by-product of forced response, which may or may not be appropriate.
Do you label them with numbers? If you do, is the neutral category a zero? Compare: "1 Don't like it at all / 2 / 3 / 4 / 5 Like it a lot" vs "-2 Don't like it at all / -1 / 0 / 1 / 2 Like it a lot". The latter one does have the swing from negative to positive attitude, while the former one does not.
If you provide text with the categories, are they equidistant? Netflix 5-star scale sucks, in my opinion: it has only 1 star for "Don't like"s, and between 3 and 5 stars for various degree of "Like"s. Our department teaching evaluations were like that, too: 1 for "Poor", 2 for "Adequate", 3 for "Good", 4 for "Excellent", 5 for "Outstanding", and you basically had to score 4 and above. That's where most of the inconsistencies in validation will likely come from, as the distance between 4 and 5 is not nearly the same as between 1 and 2.
Update: As far as reliability and validity are concerned, I am not sure as to what the standard practices are regarding Likert scales. You can probably present the analysis of both the moment covariance and polychoric correlation matrices, to demonstrate the factor structure, reliability of individual items, and composite reliability of the factor. The moment-based analysis will understate the reliability of the underlying continuous scales, as much work has shown; the polychoric correlations will get these continuous scales right, but that's not what you are measuring. So the true reliability of your measurement process is somewhere in between. You can also demonstrate discriminant validity with these internal measurements (different factors correspond to different concepts, and hence their correlation is less than 1). To demonstrate external validity in its strongest form, you would need some additional behavioral variables coming from a substantive model. E.g., if a certain physical activity is "difficult" to do in the old age, you would expect it to be done "rarely".
Best Answer
In general what and how you intend to use the questionnaire makes a difference in practice. I have often only used 5 points because my subjects were often quite busy in daily life and return rates were higher with 5 points. With 7 points you get more data and I would think that might help in situations with low sample size.
I cannot find the actual paper, but this practical source might be helpful.
I might need to add, that I have not been doing many surveys in the last couple of years. The state of the art might have advanced and I am unaware of that...