Research Article
Evaluating the Longitudinal Item and Category Stability of the SF-36 Full and Summary Scales Using Rasch Analysis
Table 16
SF-36 mental health 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 | 38.55 | 100.00% | 100.00% | 41.29 | 100.00% | 100.00% | 42.62 | 100.00% | 100.00% | | Raw variance explained by measures | 24.55 | 63.70% | 63.70% | 27.29 | 66.10% | 66.20% | 26.62 | 62.50% | 62.50% | | Raw variance explained by persons | 2.85 | 7.40% | 7.40% | 2.06 | 5.00% | 5.00% | 2.68 | 6.30% | 6.30% | | Raw Variance explained by items | 21.70 | 56.30% | 56.30% | 25.23 | 61.10% | 61.20% | 23.94 | 56.20% | 56.20% | | Raw unexplained variance (total) | 14.00 | 36.30% | 36.30% | 14.00 | 33.90% | 33.80% | 16.00 | 37.50% | 37.50% | | Unexplained variance in 1st contrast | 6.22 | 16.10% | 44.50% | 6.22 | 15.10% | 44.40% | 7.02 | 16.50% | 43.90% | | Unexplained variance in 2nd contrast | 1.49 | 3.90% | 10.60% | 1.47 | 3.60% | 10.50% | 1.62 | 3.80% | 10.10% | | Unexplained variance in 3rd contrast | 1.29 | 3.30% | 9.20% | 1.32 | 3.20% | 9.40% | 1.29 | 3.00% | 8.10% | | Unexplained variance in 4th contrast | 0.81 | 2.10% | 5.80% | 0.85 | 2.00% | 6.00% | 1.05 | 2.50% | 6.60% | | Unexplained variance in 5th contrast | 0.68 | 1.80% | 4.90% | 0.71 | 1.70% | 5.00% | 0.71 | 1.70% | 4.40% |
| | | WAVE 4 | WAVE 5 | WAVE 6 | | | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected | Eigenvalue | Observed | Expected |
| | Total raw variance in observations | 39.19 | 100.00% | 100.00% | 37.79 | 100.00% | 100.00% | 37.65 | 100.00% | 100.00% | | Raw variance explained by measures | 25.19 | 64.30% | 64.50% | 23.79 | 62.90% | 63.30% | 23.65 | 62.80% | 63.20% | | Raw variance explained by persons | 2.43 | 6.20% | 6.20% | 1.73 | 4.60% | 4.60% | 2.44 | 6.50% | 6.50% | | Raw Variance explained by items | 22.76 | 58.10% | 58.30% | 22.06 | 58.40% | 58.70% | 21.21 | 56.30% | 56.60% | | Raw unexplained variance (total) | 14.00 | 35.70% | 35.50% | 14.00 | 37.10% | 36.70% | 14.00 | 37.20% | 36.80% | | Unexplained variance in 1st contrast | 6.16 | 15.70% | 44.00% | 6.10 | 16.10% | 43.60% | 5.75 | 15.30% | 41.10% | | Unexplained variance in 2nd contrast | 1.52 | 3.90% | 10.90% | 1.61 | 4.20% | 11.50% | 1.67 | 4.40% | 11.90% | | Unexplained variance in 3rd contrast | 1.32 | 3.40% | 9.40% | 1.31 | 3.50% | 9.30% | 1.35 | 3.60% | 9.60% | | Unexplained variance in 4th contrast | 0.80 | 2.00% | 5.70% | 0.79 | 2.10% | 5.60% | 0.85 | 2.30% | 6.10% | | Unexplained variance in 5th contrast | 0.68 | 1.70% | 4.90% | 0.69 | 1.80% | 4.90% | 0.68 | 1.80% | 4.80% |
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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. |
