Thurstone scale is associated with the name of L. L. Thurstone. In this scale, several statements, whose position on the scale has been determined by judges, is used. The position is determined by the method of equal-appearing intervals. The procedure is as follows:
At first, a reasonably large number of statements relating to the attitudes to be studied are collected. A large number of judges work independently to classify these statements into 11 groups.
In the first group, all the statements which are most unfavorable to the issue are placed. The next unfavorable statements are placed in the second group, and so on. The statements of the 11th group are considered most favorable.
The sixth position (the middle one) on this continuum is the point at which the attitude is neutral. The first group is given a score of 11, and the 11th group the score I.
The scale-value of a statement is computed as the mean or median position to which it is assigned by the judges. Statements that are ambiguous, vague, or irrelevant and over which judges differ widely are discarded.
Finally, the scale is prepared by taking into account the evaluated statements that spread out evenly from one extreme to the other.
Suppose that a statement (say A) has been distributed to 50 judges into 11 categories as follows:
We treat the statements as variable values (x) and the number of judges as frequencies (f), and calculate the mean value as follows:
The median score is computed to be 5. If we choose the median, then the scale value of statement A is 5. In a similar manner, every item is assigned a numerical score.
Thurstone scale consists, thus, of a series of statements whose positions have been determined neutrally by the judges.
At the time of administration of the scale questionnaire, the respondents are asked to check the statements with which they agree.
Like the Likert scale, the scale values are not shown in the questionnaire, and the statements are arranged randomly.