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The numeric values of the categories (item scale steps) represent measurement on an ordinal scale – they only indicate relative order along the able-not able (or not participating-participating) continuum, but the differences between scale steps are not equivalent, and the values chosen for them are arbitrary. As a result, adding up the scores for the items to obtain the total score is not an operation that is allowed, based on the rules of mathematics. Therefore, total scores do not reflect position along a continuum that has a true zero point, and constant distances between scale points. (These constitute the definition of a ratio scale, which is what is required for calculating means for a group, or percentage improvement over time). However, research has shown that if the item category values are chosen “reasonably”, the sum of ordinal items corresponds quite well to values on a true ratio scale, at least for intermediate levels of the continuum of total scores (26). Rasch analysis, a mathematical procedure based on Item Response Theory (IRT) has been used to transform a set of scores on ordinal FA items into a score on an interval scale (10, 21, 26). The theoretical assumptions and mathematical manipulations underlying Rasch Analysis-based FA instruments are beyond the scope of this chapter; good introductions to the technique and its application to FA may be found in Bond and Fox (27). |
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请问哪里可以有青B申请的本子可以借鉴一下。
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