in Rasch Model：在Rasch模型.ppt

Rating Scale Model Can be considered as a particular case of PCM when all items have the common response format (for example, Likert scale) Usually is used to collect attitude data Each item is provided with a stem (or statement of attitude) and a few response alternatives where a respondent is required to chose one, indicating the extent to which the statement in the stem is endorsed Thus, all items have m response alternatives and they are the same for all items. Completing of the k-th step can be considered as choosing the k-th alternative over the (k-1)-th in response to the item. Example: Likert Scale Has 4 or 5 categories: Strongly Disagree, Disagree, Undecided (or Neutral) - may be omitted, Agree, Strongly Agree: SD D N A SA Response alternatives are ordered to represent a respondent’s increasing inclination towards the concept questioned A person who chooses to Agree with a statement on an attitude questionnaire can be considered to have chosen Disagree over Strongly Disagree (1-st step taken), and also Neutral over Disagree (2-nd step taken), and also Agree over Neutral (3-rd step taken), but to have failed to choose Strongly Agree over Agree (4-th step not taken). All responses are coded as 1,2,3,4,5, where the higher number indicates a higher degree of agreement with the statement. Concept of item difficulty Consider two statements from the test of computer anxiety : I am so afraid of computers I avoid using them SD D N A SA I am afraid that I’ll make mistakes when I use my computer SD D N A SA It is more than likely that the first stem indicates much higher levels of computer anxiety that does the second stem. Indeed, the children who respond SA on the “mistakes” stem might endorse N on the “avoid using” stem. And we should use : I am so afraid of computers I avoid using them SD D N A SA I am afraid that I’ll make mistakes wh