# Need someone who know statistics

Assignment 5, Part A

The Measurement Model

1. Using the Rasch formula what is the probability of getting an item right for a person with a theta of 4 assuming an item difficulty, delta, of 3 (show all work).

2. Open the data in the folder pf10_dich.   What is the estimated theta for the person with research id:   716405B (look in Name column).

3. Compare this person’s theta (person 716405B) with all of the item deltas.  Which items would you expect this person to get a 1 score  at least 50% of the time?

4. Compare this person’s theta (person 9413932) with all of the item deltas.  Which items would you expect this person to get a 1 score at least 50% of the time?

5. Which item (or items) is the most difficult and which item (or items) is the easiest.

6. Which item seems to be problematic in terms of not fitting the Rasch Model very well.  (Use the outfit statistic).  How would you describe this item using variable screening methods for skewness and kurtosis.  Any evidence for floor or ceiling effects.

7.  For the item identified in #7, what does the infit value suggest with respect to this item. Is the item contributing less to the overall estimate of the thetas in the sample than the other items that are not problematic in terms of fit to the Rasch Model.  Does this value suggest that the outfit value for this item was perhaps not so bad afterall.

8. Please use dataset “for HW 3 and 4.xls”.  This is an excel file.  Enter this data into the ConstructMap software.  Cutting and pasting saves time.  Create names for the variables.  Pretend this dataset was obtained from a measure in your research area of interest:

a. List each of the 10 variables.

b. What construct does this hypothetical instrument measure.

c. Run a Rasch Model analysis for these data.

d. Report the average theta value (you may need to copy the thetas into SPSS).

e. Using the Wright Map, which item would you expect only the highest theta

individuals to obtain a 1 over 50% of the time?  What else can you do to see if this item is indeed a very hard item?

Assignment 5, Part B

1. Please find an article that includes use of IRT.  Please make sure the article answers a substantive research question or research questions in your area of interest….Do not use an article that focuses on some theoretical issue pertaining to how to improve the estimation or use of IRT.  In other words, the article should focus on your research interests and should be applied in nature.   Provide the following information about the article.

a. Please upload into Blackboard a  .pdf of the article that you choose to review along with your homework assignment.

b.  State the research questions that were examined in the study.

d. How did the author/s go about using IRT?  Give details such as the type of model, calibration, the scores that were obtained, etc.

e. What conclusions were drawn from the IRT analysis?  Include a statement concerning how the IRT analysis enabled the researcher/s to answer the research questions.

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