Reliability, Validity and Fit

1. Reliability, Validity and Fit

2. Functional Independence Measure (FIM): Example 17s • In Example 17, 35 arthritis patients have been through rehabilitation therapy. Their admission to therapy and discharge from therapy measures are to be compared. They have been rated on 18 items of the Functional Independence Measure (FIM™). Each item has seven levels. A prime concern is to measure the change of patient disability from admission to discharge. First, we need to check validity and reliability. • Here, admission and discharge measures are placed together (“stacked”)

3. Looking at the Diagnostics • What information does this table provide? • How do we read it? • What do we learn about these data? • Item Fit • Person Keyforms • Summary Statistics • Variable Map • Probability Curves • Dimensionality Map • (Table 7.1- Person Responses) • (Table 2:2- General Keyform)

4. The Structure and Stability of the Functional Independence Measure (FIM) http://www.rasch.org/memo50.htm • Cites sources regarding deficiencies of raw score analysis of scales http://www.rasch.org/rmt/rmt103e.htm • Defends use of Rasch to analyze these data for a critic

5. Another option for checking comparability • In Winsteps • Exam12.txt • Start by copying exam12.txt information and pasting it in exam12lo.txt control file. Save to desktop. • Do the same for exam12hi.txt • Run each of the analyses in Winsteps.

6. Export Measures to Excel • Output Files  Item File • Display with Excel • File format: Text: tab-delimited (best for Excel) • Column Headings: Include • Insert  Chart  Scatter • Put cursor in “Data Range” box, then highlight columns in worksheet. • OR you could create a scatterplot in Minitab

7. This concept can be applied elsewhere • Comparing people over time (how much people improve after intervention) • Comparing items over time (how much easier items become after intervention) • “Rack and Stack” Example: www.raschsig.org/rmt171.pdf

8. To look at person change: Stack • Items are modeled to maintain their difficulties across the two time points, and the persons are entered twice, once at admission to rehabilitation and once at discharge from it. • Changes in patient independence can be identified by cross-plotting the admission and discharge measures for each patient, as in example 12 or looking at the difference in measures Time 1 Time 2

9. To look at item change: Rack • To look at WHAT has changed instead of WHO has changed. • Items are entered twice, once at admission to rehabilitation and once at discharge from it. Items Items(again) Time 1 Time 2 Persons