Table 1.
Descriptive Statistics of Time-Varying and Time-Constant Covariates
| Time-varying covariates | 1998 (n = 14,553) | 2000 (n = 16,543) | 2002 (n = 14,587) | 2004 (n = 13,352) | 2006 (n = 12,089) |
| Functional status | 0.62 ± 1.74 | 0.56 ± 1.63 | 0.76 ± 1.80 | 0.78 ± 1.81 | 0.74 ± 1.77 |
| Time since baseline (in years) | 2.37 ± 0.48 | 3.79 ± 1.07 | 5.75 ± 1.06 | 7.71 ± 1.05 | 9.68 ± 1.03 |
| Proxy status (lagged), n (%) | 932 (6) | 1,074 (6) | 997 (7) | 948 (7) | 695 (6) |
| Change in proxy status (since last interview) | 0.02 ± 0.22 | 0.02 ± 0.20 | 0.01 ± 0.21 | −0.001 ± 0.20 | −0.01 ± 0.20 |
| Marital status (lagged), n (%) | 10,496 (72) | 11,756 (71) | 9.894 (68) | 8,910 (67) | 7,964 (66) |
| Change in marital status (since last interview) | −0.02 ± 0.14 | −0.05 ± 0.26 | −0.03 ± 0.21 | −0.02 ± 0.20 | −0.03 ± 0.20 |
| Self-rated health (lagged) | 2.71 ± 1.14 | 2.85 ± 1.14 | 2.74 ± 1.11 | 2.79 ± 1.09 | 2.84 ± 1.09 |
| Change in self-rated health (since last interview) | 0.26 ± 0.94 | −0.03 ± 0.92 | 0.11 ± 0.90 | 0.12 ± 0.88 | 0.07 ± 0.88 |
| Diseases (lagged) | 1.56 ± 1.22 | 1.63 ± 1.25 | 1.71 ± 1.25 | 1.86 ± 1.27 | 1.99 ± 1.29 |
| Change in diseases (since last interview) | 0.21 ± 0.57 | 0.14 ± 0.59 | 0.21 ± 0.61 | 0.18 ± 0.61 | 0.17 ± 0.60 |
| Depressive symptoms (lagged) | 1.76 ± 1.96 | 1.98 ± 2.11 | 1.94 ± 2.09 | 1.90 ± 2.13 | 1.83 ±2.11 |
| Change in depressive symptoms (since last interview) |
0.39 ± 2.04 |
0.06 ± 2.03 |
0.04 ± 2.02 |
0.03 ± 2.00 |
0.11 ± 1.95 |
| Time-constant covariates |
Total (N = 18,486) |
White (n = 14,552) |
Black (n = 2,567) |
Hispanic (n = 1,367) |
p Value |
| Died (between baseline and 2006), n (%) | 4,755 (26) | 3,704 (25) | 731 (28) | 320 (23) | .0007 |
| Ever attrited (between baseline and 2006), n (%) | 1,705 (9) | 1,248 (9) | 295 (11) | 162 (12) | <.0001 |
| Female, n (%) | 10,505 (57) | 8,124 (56) | 1,603 (62) | 778 (57) | <.0001 |
| Age (years, in 1995) | 64.28 ± 10.23 | 64.57 ± 10.23 | 63.31 ± 10.25 | 62.94 ± 9.84 | <.0001 |
| Education | 11.94 ± 3.37 | 12.54 ± 2.82 | 10.63 ± 3.64 | 8.04 ± 4.67 | <.0001 |
| Baseline marital status, n (%) | 13,222 (72) | 10,892 (75) | 1,369 (53) | 961 (70) | <.0001 |
| Baseline proxy interview status, n (%) | 1,148 (6) | 805 (6) | 184 (7) | 159 (12) | <.0001 |
| Baseline self-rated health | 2.70 ± 1.15 | 2.59 ± 1.12 | 3.09 ± 1.14 | 3.17 ± 1.18 | <.0001 |
| Baseline diseases | 1.52 ± 1.22 | 1.48 ± 1.21 | 1.78 ± 1.24 | 1.42 ± 1.22 | <.0001 |
| Baseline depressive symptoms | 1.76 ± 1.97 | 1.61 ± 1.85 | 2.21 ± 2.17 | 2.51 ± 2.43 | <.0001 |
| Baseline ADL/IADL | 0.42 ± 1.36 | 0.34 ± 1.21 | 0.73 ± 1.80 | 0.69 ± 1.77 | <.0001 |
Notes: Statistics are reported as mean ± standard deviation or n (%). Time-varying covariates are those associated with repeated observations within individuals. Data based on the 1995–2006 Health and Retirement Study. ADL = activities of daily living; IADL = instrumental activities of daily living.
*p < .05; **p < .01; ***p < .001.