Thurstone scale (method of equal-appearing intervals)

The method of equal-appearing intervals or the Thurstone scale is used to measure attitudes of people. Logframer allows you to use a Thurstone scale to measure an indicator, but developing such a scale is not so simple.

This kind of scale is used to measure people's attitude towards a fairly clear and unidimensional concept, using a number of statements that vary in how they express a positive or negative opinion about the main concept. We'll briefly explain the steps of developing a Thurstone scale:

  1. Determine the focus: what concept are you going to measure (see what people's attitudes are toward it)?
  2. Ask a group of people (or a person) to write down different statements about this concept, reflecting different opinions or attitudes about the subject. Make sure you have a large number of statements, making sure that people can either degree or disagree with them (no - open - questions for instance).
  3. Rating the scale items: the next step is to have your group rate each statement on a 1-to-11 scale in terms of how much each statement indicates a favourable attitude towards the concept. The members of the group must not express their own opinion, they must only indicate how favourable they feel each statement is. You can use a scale with 1 = extremely favourable attitude towards the subject (focus) and 11 = extremely unfavourable attitude towards the subject.
  4. Compute the median and interquartile range for each statement. Create a table with these values and sort by the median.
  5. Select the items for the actual scale: you should select statements that are at equal intervals across the range of medians. Within each value, you should try to select the statement that has the smallest Interquartile Range. This is the statement with the least amount of variability across judges. You don't want the statistical analysis to be the only deciding factor here. Look over the candidate statements at each level and select the statement that makes the most sense. If you find that the best statistical choice is a confusing statement, select the next best choice.

For a detailed example, see


You can now use the scale to measure attitudes 'in the field': enter the list of statements and use them to interview people or present them in a document. For each item, they should express whether they agree or disagree. The total score of a person is calculated by making the sum of the values of all the statements they agreed with, divided by the number of items he agreed on (in other words, the average of the statements they agreed with).

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