0 10 20 30 40 50 | 60 70 80 90 100 HARDER ITEMS
|-----+-----+-----+-----+-----+-----+-----+-----+-----+-----|
| | [0] : 1 16. when admitted here
| | [0] : 1 | 15. details on first memory
| | [0] : 1 | 14. detail on last memory
| [0] : 1 | 13. got here how
| [0]| : 1 | 12. first memory after injury
| 0 | : [1] | 11. last memory before injury
| 0 | : [1] | 10. day of month-now
| 0 : | [1] | 9. time-now
| [0] : |1 | 8. day of week-now
| 0 : [1] | 7. where now-hospital
| 0 : [1] | 5. month-now
| 0 : [1] | | 4. where now-city
| 0 : [1] | | 3. year-now
| | |
| [0] : 1| | 6. when born
| 0 : [1] | | 2. where live
0 : [1] | | 1. name
|-----+-----+-----+-----+-----+-----+-----+-----+-----+-----|
0 10 20 30 40 50 | 60 70 80 90 100 EASIER ITEMS
<-- More Impaired | Less Impaired -->
Person Measure
| Score on GOAT | Patient Measure |
Guttman Item Location | Item |
| 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
0 (Extreme) 7 18 25 31 36 40 45 49 53 58 62 67 72 79 89 97 (Extreme) |
0 (Extreme) 12 22 28 33 38 42 47 51 55 60 64 69 75 84 97 (Extreme) |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
| Table 1. Measures and Locations | |||
Guttman and the KeyGoat Self-scoring Form
Constructing a self-scoring form for dichotomous items is a challenge. For rating scales, category expectations provide useful locations for the rating points, e.g., KeyFIM (RMT 9:3, p. 454). To generate these, I use WINSTEPS, Table 2:2. With dichotomous items, however, the category expectations are infinite. Finite approximations, used in Figure 1 (the KeyGOAT), do not lead to a practical self scoring form. There is no simple way to see an estimate measures from circled item responses.
Guttman to the rescue! A Guttman-style item location map (RMT 10:2 p. 492) uses response-level information in different way. To construct such a map, produce a score-to-measure conversion table for the complete test. Order the test items by measure. Then advance through the person measure table placing the items, in order, at about halfway between the patient measures. This constructs the linear equivalent of a scalogram. The median position along the line that minimizes reversals estimates the person measure. For short tests, impute missing responses based on your clinical knowledge of the patients.
Table 1 is the score-to-measure conversion table for the KeyGoat. The Guttman locations of the 16 items are also shown. The extreme items are located at the extreme person measures; other items are located midway between the person measures. The corresponding KeyGoat is shown in Figure 2. In each response box, when correct, and when incorrect. The median (not average) location which balances the number of successes and failures corresponds to the person measure. As with other self-scoring forms unexpected responses and aberrant patterns are immediately obvious.
Rita Bode
Rehabilitation Institute of Chicago
Self-Scoring Guttman-style KeyGOAT
0 10 20 30 40 50 | 60 70 80 90 100 HARDER ITEMS
|-----+-----+-----+-----+-----+-----+-----+-----+-----+-----|
| | 0 | 16. when admitted here
| | 0 | 15. details on first memory
| | 0 | 14. detail on last memory
| | 0 | 13. got here how
| | 0 | 12. first memory after injury
| | 1 | 11. last memory before injury
| |1 | 10. day of month-now
| 1 | | 9. time-now
| 0 | | 8. day of week-now
| 1 | | 7. where now-hospital
| 1 | | 5. month-now
| 1 | | 4. where now-city
| 1 | | 3. year-now
| | |
| 0 | | 6. when born
| 1 | | 2. where live
1 | | 1. name
|-----+-----+-----+-----+-----+-----+-----+-----+-----+-----|
0 10 20 30 40 50 | 60 70 80 90 100 EASIER ITEMS
<-- More Impaired | Less Impaired -->
Patient Measure
Self-Scoring Key for Galveston Orientation and Amnesia Text Bode, R. … Rasch Measurement Transactions, 1999, 13:1 p. 680
| Rasch Publications | ||||
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| Rasch Measurement Transactions (free, online) | Rasch Measurement research papers (free, online) | Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch | Applying the Rasch Model 3rd. Ed., Bond & Fox | Best Test Design, Wright & Stone |
| Rating Scale Analysis, Wright & Masters | Introduction to Rasch Measurement, E. Smith & R. Smith | Introduction to Many-Facet Rasch Measurement, Thomas Eckes | Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr. | Statistical Analyses for Language Testers, Rita Green |
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