Table 3.
Linear Mixed Effect Models of the Association of Baseline Fatigability and Longitudinal Change in Fatigability with Change in Cognitive Test Scores Over Time
| Model 1 | Model 2 | |||||
|---|---|---|---|---|---|---|
| β (SE) | z | p | β (SE) | z | p | |
| Memory | ||||||
| CVLT immediate recall (n = 912) | ||||||
| Change in Fatigabilitya × Time | −.06 (.05) | −1.21 | .23 | −.06 (.05) | −1.23 | .22 |
| Baseline Fatigability × Time | −.13 (.03) | −3.84 | <.001* | −.13 (.03) | −3.74 | <.001* |
| Timeb | .15 (.11) | 1.36 | .17 | .15 (.11) | 1.31 | .19 |
| CVLT long recall (n = 910) | ||||||
| Change in Fatigability × Time | −.01 (.02) | −0.59 | .56 | −.01 (.02) | −0.60 | .55 |
| Baseline Fatigability × Time | −.01 (.01) | −1.21 | .23 | −.01 (.01) | −1.13 | .26 |
| Timeb | −.05 (.03) | −1.57 | .12 | −.06 (.03) | −1.81 | .07 |
| Executive functions | ||||||
| Trails Part B (n = 907) | ||||||
| Change in Fatigability × Time | .42 (.23) | 1.85 | .06 | .46 (.23) | 2.04 | .04* |
| Baseline Fatigability × Time | .37 (.14) | 2.56 | .01* | .33 (.14) | 2.28 | .02* |
| Timeb | .32 (.48) | 0.68 | .50 | .40 (.47) | 0.85 | .40 |
| Delta TMT (n = 906) | ||||||
| Change in Fatigability × Time | .34 (.22) | 1.51 | .13 | .37 (.22) | 1.66 | .10 |
| Baseline Fatigability × Time | .22 (.14) | 1.57 | .12 | .17 (.14) | 1.27 | .20 |
| Timeb | .30 (.45) | 0.66 | .51 | .39 (.45) | 0.87 | .39 |
| Digit Span Backward (n = 926) | ||||||
| Change in Fatigability × Time | −.03 (.01) | −2.52 | .01* | −.03 (.01) | −2.51 | .01* |
| Baseline Fatigability × Time | −.01 (.01) | −1.02 | .31 | −.01 (.01) | −0.90 | .37 |
| Timeb | −.04 (.03) | −1.33 | .19 | −.04 (.03) | −1.55 | .12 |
| DSST (n = 906) | ||||||
| Change in Fatigability × Time | −.09 (.04) | −2.35 | .02* | −.10 (.04) | −2.54 | .01* |
| Baseline Fatigability × Time | −.07 (.03) | −2.45 | .01* | −.06 (.03) | −2.41 | .02* |
| Timeb | −1.06 (.09) | −12.04 | <.001** | −1.03 (.09) | −11.55 | <.001** |
| Language | ||||||
| Verbal fluency—categories (n = 922) | ||||||
| Change in Fatigability × Time | −.02 (.01) | −1.33 | .18 | −.02 (.01) | −1.37 | .17 |
| Baseline Fatigability × Time | −.02 (.01) | −1.66 | .10 | −.02 (.01) | −1.59 | .11 |
| Timeb | −.16 (.03) | −4.84 | <.001** | −.15 (.03) | −4.81 | <.001** |
| Verbal fluency—letters (n = 921) | ||||||
| Change in Fatigability × Time | .00 (.02) | 0.29 | .77 | .00 (.02) | 0.28 | .78 |
| Baseline Fatigability × Time | −.02 (.01) | −2.46 | .01* | −.02 (.01) | −2.44 | .02* |
| Timeb | .07 (.03) | 2.05 | .04* | .06 (.03) | 1.93 | .05 |
| Attention | ||||||
| Trails Part A (n = 919) | ||||||
| Change in Fatigability × Time | .09 (.08) | 1.10 | .27 | .11 (.08) | 1.37 | .17 |
| Baseline Fatigability × Time | .19 (.07) | 2.77 | .01* | .17 (.07) | 2.59 | .01* |
| Timeb | −.12 (.22) | −0.54 | .59 | −.12 (.22) | −0.52 | .60 |
| Digit Span Forward (n = 926) | ||||||
| Change in Fatigability × Time | −.01 (.01) | −0.60 | .55 | −.01 (.01) | −0.63 | .53 |
| Baseline Fatigability × Time | −.01 (.01) | −1.31 | .19 | −.01 (.01) | −1.20 | .23 |
| Timeb | −.03 (.03) | −1.11 | .27 | −.04 (.03) | −1.36 | .18 |
Note: Model 1: unadjusted; Model 2: adjusted for interaction main effects (change in fatigability, baseline fatigability, and time), age, sex, race, years of education, comorbidities, and body mass index; CVLT = California Verbal Learning Test.; TMT = Trail Making Test; DSST = Digit Symbol Substitution Test.
aFatigability units are in rating of perceived exertion total score: sample range 6–19.
bTime is interpreted when change in fatigability = 0, baseline fatigability = 6, and age = 70.
*p < .05.
**p < .001.