Table 2.
Internal validity assessment: equivalence of study groups 1–5 at completion of the baseline survey*
| Independent variables | Group 1, n (%) | Group 2, n (%) | Group 3, n (%) | Group 4 (delayed 1 y), n (%) |
Group 5 (delayed 2 y), n (%) |
P† |
|---|---|---|---|---|---|---|
| Study candidate status | .001 | |||||
| Nonrespondents | 530 (27.1) | 527 (26.3) | 529 (26.8) | 669 (32.0) | 556 (29.5) | |
| Postrandomization refusals at baseline |
309 (15.8) | 307 (15.3) | 317 (16.1) | 330 (15.8) | 308 (16.4) | |
| Eligible respondents | 1116 (57.1) | 1169 (58.4) | 1129 (57.2) | 1091 (52.2) | 1020 (54.1) | |
| Survey response mode | <.001 | |||||
| 960 (86.0) | 968 (82.8) | 981 (86.9) | 997 (91.4) | 906 (88.8) | ||
| Phone | 156 (14.0) | 201 (17.2) | 148 (13.1) | 94 (8.6) | 114 (11.2) | |
| Race/ethnicity | .342 | |||||
| African American | 79 (7.1) | 89 (7.6) | 77 (6.8) | 76 (7.0) | 74 (7.3) | |
| Hispanic | 42 (3.8) | 25 (2.1) | 29 (2.6) | 42 (3.9) | 29 (2.8) | |
| Non-Hispanic white | 953 (85.4) | 994 (85.0) | 975 (86.4) | 929 (85.2) | 871 (85.4) | |
| Unknown | 42 (3.8) | 61 (5.2) | 48 (4.3) | 44 (4.0) | 46 (4.5) | |
| Educational level | .687 | |||||
| High school or less | 165 (14.8) | 176 (15.1) | 156 (13.8) | 163 (14.9) | 139 (13.6) | |
| Some college | 471 (42.2) | 512 (43.8) | 518 (45.9) | 467 (42.8) | 449 (44.0) | |
| College graduate or higher | 441 (39.5) | 442 (37.8) | 429 (38.0) | 447 (41.0) | 420 (41.2) | |
| Unknown | 39 (3.5) | 39 (3.3) | 26 (2.3) | 14 (1.3) | 12 (1.2) | |
| Ever used VA health- care services |
.138 | |||||
| Yes | 452 (40.5) | 431 (36.9) | 434 (38.4) | 450 (41.3) | 420 (41.2) | |
| No | 664 (59.5) | 738 (63.1) | 695 (61.6) | 641 (58.7) | 600 (58.8) | |
| Sampling round ‡ | .645 | |||||
| 1 | 594 (53.2) | 616 (52.7) | 602 (53.3) | 608 (55.7) | 552 (54.1) | |
| 2 | 522 (46.8) | 553 (47.3) | 527 (46.7) | 483 (44.3) | 468 (45.9) | |
| Age, y§ | .532 | |||||
| 52–64 | 728 (65.2) | 789 (67.5) | 726 (64.3) | 720 (66.0) | 681 (66.8) | |
| ≥ 65 | 388 (34.8) | 380 (32.5) | 403 (35.7) | 371 (34.0) | 339 (33.2) | |
*
Groups 4 and 5 received the baseline survey 1 and 2 years, respectively, after groups 1–3. VA = Veterans Administration.
†
From two-sided chi-square tests.
‡
Sampling round 1 occurred on September 4, 2000 (with follow-up through December 17, 2003); sampling round 2 occurred on June 1, 2001 (with follow-up through October 1, 2004).
§
Age at baseline survey mail date.