How we change what others think, feel, believe and do
A Thurstone scale has a number of statements to which the respondent is asked to agree or disagree.
There are three types of scale that Thurstone described:
In this method, the judges select between every possible pair of potential statements. As the number of comparisons increases with the square of the number of statements, this is only practical when there is a limited number of statements.
Judges are used beforehand to understand variation -- if the judge cannot agree, then the question as posed is also likely to result in varied responses from target people.
One of the biggest problem with Thurstone scaling is to find sufficient judges who have a good enough understanding of the concept being assessed.
With a set of questions with which you can agree or not, it is useful to have some questions with which the respondent will easily agree, some with which they will easily disagree and some which they have to think about, and where some people are more likely to make one choice rather than another. This should then give a realistic and varying distribution across all questions, rather than bias being caused by questions that are likely to give all of one type of answer.
Thurstone scaling is also called Equal-Appearing Interval Scaling.