If I collect data using a Likert-scale type questionnaire with ratings from strongly agree (5) to strongly disagree (1), can I convert the responses into numerical scores (interval data) and perform any parametric tests on the data? I will appreciate reference to standard literature. Thank you.
There are three grades of data here:
* categorical data: incomparable categories (apples and oranges)
* ordinal data: like you have, allows comparisons like "more than"
* interval data: allows comparisons like "25% more"
A Likert scale does not really give you interval data. It doesn't feel very sound to say that people who give a score of 6 agree 20% more than people who give a score of 5.
However, you could normalize the data by monotonic regression - then the tests you want to make would feel more appropriate.
Yes, we can!
Ordinal data are the most frequently encountered type of data in the social sciences. Many statistical methods can be used to process such data. One common method is to assign scores to the data, convert them into interval data, and further perform statistical analysis.
Ordinal data are most concerned about the order and ranking while interval data are concerned about the differences of value within two consecutive values. 2. Ordinal data place an emphasis on the position on a scale while interval data are on the value differences of two values in a scale.
Here is the source and you can refer it for further understanding
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