Research Article
Evaluating the Longitudinal Item and Category Stability of the SF-36 Full and Summary Scales Using Rasch Analysis
Table 4
SF-36 total scale Rasch analysis of standardised residual variance in Eigenvalue units for six waves of data collection.
| | | Wave 1 | Wave 2 | Wave 3 | | | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected |
| | Total raw variance in observations | 86.71 | 100.00% | 100.00% | 92.22 | 100.00% | 100.00% | 92.42 | 100.00% | 100.00% | | Raw variance explained by measures | 50.71 | 58.50% | 58.70% | 56.22 | 61.00% | 61.10% | 56.42 | 61.00% | 61.30% | | Raw variance explained by persons | 3.47 | 4.00% | 4.00% | 1.93 | 2.10% | 2.10% | 2.04 | 2.20% | 2.20% | | Raw Variance explained by items | 47.24 | 54.50% | 54.70% | 54.30 | 58.90% | 59.00% | 54.38 | 58.80% | 59.10% | | Raw unexplained variance (total) | 36.00 | 41.50% | 41.30% | 36.00 | 39.00% | 38.90% | 36.00 | 39.00% | 38.70% | | Unexplained variance in 1st contrast | 12.60 | 14.50% | 35.00% | 12.57 | 13.60% | 34.90% | 12.26 | 13.30% | 34.10% | | Unexplained variance in 2nd contrast | 3.02 | 3.50% | 8.40% | 3.05 | 3.30% | 8.50% | 3.03 | 3.30% | 8.40% | | Unexplained variance in 3rd contrast | 1.89 | 2.20% | 5.20% | 1.78 | 1.90% | 4.90% | 1.84 | 2.00% | 5.10% | | Unexplained variance in 4th contrast | 1.59 | 1.80% | 4.40% | 1.54 | 1.70% | 4.30% | 1.50 | 1.60% | 4.20% | | Unexplained variance in 5th contrast | 1.24 | 1.40% | 3.40% | 1.27 | 1.40% | 3.50% | 1.26 | 1.40% | 3.50% |
| | | Wave 4 | Wave 5 | Wave 6 | | | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected |
| | Total raw variance in observations | 92.10 | 100.00% | 100.00% | 91.96 | 100.00% | 100.00% | 94.92 | 100.00% | 100.00% | | Raw variance explained by measures | 56.10 | 60.90% | 61.50% | 55.96 | 60.90% | 61.70% | 58.92 | 62.10% | 63.00% | | Raw variance explained by persons | 3.59 | 3.90% | 3.90% | 4.05 | 4.40% | 4.50% | 4.57 | 4.80% | 4.90% | | Raw Variance explained by items | 52.51 | 57.00% | 57.60% | 51.91 | 56.40% | 57.20% | 54.35 | 57.30% | 58.10% | | Raw unexplained variance (total) | 36.00 | 39.10% | 38.50% | 36.00 | 39.10% | 38.30% | 36.00 | 37.90% | 37.00% | | Unexplained variance in 1st contrast | 12.41 | 13.50% | 34.50% | 12.08 | 13.10% | 33.60% | 11.33 | 11.90% | 31.50% | | Unexplained variance in 2nd contrast | 3.06 | 3.30% | 8.50% | 3.20 | 3.50% | 8.90% | 3.22 | 3.40% | 8.90% | | Unexplained variance in 3rd contrast | 1.88 | 2.00% | 5.20% | 1.95 | 2.10% | 5.40% | 2.17 | 2.30% | 6.00% | | Unexplained variance in 4th contrast | 1.50 | 1.60% | 4.20% | 1.53 | 1.70% | 4.30% | 1.55 | 1.60% | 4.30% | | Unexplained variance in 5th contrast | 1.27 | 1.40% | 3.50% | 1.25 | 1.40% | 3.50% | 1.30 | 1.40% | 3.60% |
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Notes. > 60% unexplained variance in the Rasch factor; Eigenvalue in the first contrast <3.0; < 10% unexplained variance in the first contrast. |
