How we change what others think, feel, believe and do

Thurstone scale

Explanations > Social Research > Measurement > Thurstone scale

Description | Example | Question selection | Discussion | See also

Description

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:

• Equal-appearing intervals method
• Successive intervals method
• Paired comparisons method

Example

Question selection

Equal-appearing intervals

1. Generate a large set of possible statements.
2. Get a set of judges to rate the statements in terms of how much they agree with them, from 1 (agree least) to 11 (agree most).
3. For each statement, plot a histogram of the numbers against which the different judges scored it.
4. For each statement, identify the median score, the number below 25% (Q1) and below 75% (Q3). The difference between these is the interquartile range.
5. Sort the list by median value (This is the 'common' score in terms of agreement).
6. Select a set of statements that are are equal positions across the range of medians. Choose the one with the lowest interquartile range for each position.

Successive intervals

Paired comparisons

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.

Discussion

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.

See also

http://www.brocku.ca/MeadProject/Thurstone/Thurstone_1952.html