Introduction
Methods
Participants
Design
Interventions
Tailored Print Communication
Telephone Motivational Interviewing
Measurement
Process Evaluation
Statistical Analyses
Baseline Differences
Selective Dropout
Intervention Effects
Missing Values and Data Checking
Results
Baseline Characteristics
Dropout
Efficacy of TPC, TMI, and Their Combination
Primary outcomes | Baseline (mean ± SD) | Intermediate survey (week 25, mean ± SD) | Follow-up 1 (week 47, mean ± SD) | Follow-up 2 (week 73, mean ± SD) | |
---|---|---|---|---|---|
PA (hours/week) | TPC | 4.86 ± 3.98 (n = 400) | 6.92 ± 5.40 (n = 376) | 6.85 ± 5.22 (n = 266) | 5.73 ± 4.70 (n = 272) |
TMI | 4.84 ± 3.96 (n = 404) | 6.75 ± 5.17 (n = 369) | 5.67 ± 4.43 (n = 307) | 5.58 ± 4.49 (n = 302) | |
Combined | 4.31 ± 3.73 (n = 401) | 6.69 ± 5.19 (n = 370) | 6.13 ± 4.40 (n = 285) | 5.91 ± 4.55 (n = 285) | |
Control | 4.61 ± 3.63 (n = 404) | 5.92 ± 4.70 (n = 392) | 5.32 ± 4.53 (n = 331) | 5.37 ± 4.53 (n = 327) | |
Fruit intake (servings/day) | TPC | 2.16 ± 1.69 (n = 380) | 2.90 ± 1.76 (n = 376) | 3.02 ± 2.22 (n = 267) | 2.68 ± 1.81 (n = 272) |
TMI | 2.04 ± 1.55 (n = 386) | 2.90 ± 1.65 (n = 369) | 2.78 ± 2.12 (n = 307) | 2.30 ± 1.58 (n = 302) | |
Combined | 2.04 ± 1.63 (n = 385) | 2.59 ± 1.69 (n = 369) | 2.70 ± 2.09 (n = 284) | 2.28 ± 1.59 (n = 285) | |
Control | 2.10 ± 1.69 (n = 391) | 2.57 ± 1.64 (n = 392) | 2.36 ± 1.87 (n = 326) | 2.09 ± 1.58 (n = 327) | |
Vegetable intake (grams/day) | TPC | 166 ± 88 (n = 400) | 191 ± 81 (n = 376) | 205 ± 96 (n = 267) | 187 ± 92 (n = 272) |
TMI | 164 ± 81 (n = 406) | 190 ± 75 (n = 369) | 183 ± 86 (n = 310) | 175 ± 88 (n = 302) | |
Combined | 163 ± 81 (n = 404) | 181 ± 79 (n = 370) | 188 ± 86 (n = 290) | 174 ± 85 (n = 285) | |
Control | 167 ± 80 (n = 404) | 183 ± 80 (n = 392) | 176 ± 83 (n = 332) | 164 ± 81 (n = 327) |
Primary outcomes | Comparisona
| Intermediate survey (week 25) | Follow-up 1 (week 47) | Follow-up 2 (week 73) | Overall | ||||
---|---|---|---|---|---|---|---|---|---|
B (SE) | ES (95% CI) | B (SE) | ES (95% CI) | B (SE) | ES (95% CI) | B (SE) | ES (95% CI) | ||
PA in hours per week (√)c
| TPC–Control | 0.20 (0.07)** | 0.21 (0.07 to 0.35) | 0.29 (0.07)*** | 0.32 (0.16 to 0.48) | 0.08 (0.07) | 0.10 (−0.06 to 0.26) | 0.19 (0.05)*** | 0.21 (0.10 to 0.32) |
TMI–Control | 0.13 (0.07) | 0.14 (0.00 to 0.28) | 0.11 (0.07) | 0.12 (−0.03 to 0.28) | 0.10 (0.07) | 0.11 (−0.04 to 0.27) | 0.12 (0.05)* | 0.12 (0.02 to 0.23) | |
Combined–Control | 0.18 (0.07)* | 0.18 (0.04 to 0.32) | 0.25 (0.07)** | 0.27 (0.12 to 0.43) | 0.20 (0.07)** | 0.23 (0.07 to 0.38) | 0.21 (0.05)*** | 0.22 (0.11 to 0.34) | |
TPC–Combined | 0.03 (0.07) | 0.03 (−0.12 to 0.17) | 0.04 (0.07) | 0.04 (−0.11 to 0.20) | −0.11 (0.07) | −0.13 (−0.29 to 0.03) | −0.02 (0.05) | −0.02 (−0.13 to 0.09) | |
TMI–Combined | −0.04 (0.07) | −0.04 (−0.19 to 0.10) | −0.14 (0.07) | −0.15 (−0.30 to 0.00) | −0.10 (0.07) | −0.11 (−0.27 to 0.04) | −0.09 (0.05) | −0.10 (−0.21 to 0.01) | |
TPC–TMI | 0.07 (0.07) | 0.07 (−0.07 to 0.21) | 0.17 (0.07)* | 0.19 (0.04 to 0.35) | −0.01 (0.07) | −0.02 (−0.17 to 0.14) | 0.07 (0.05) | 0.08 (−0.03 to 0.19) | |
Treat–Controlb
| 0.17 (0.04)*** | 0.18 (0.09 to 0.27) | |||||||
Fruit in servings per day (√)d
| TPC–Control | 0.07 (0.03)* | 0.15 (0.03 to 0.27) | 0.16 (0.04)*** | 0.30 (0.14 to 0.46) | 0.16 (0.04)*** | 0.33 (0.17 to 0.49) | 0.10 (.02)*** | 0.20 (0.10 to 0.30) |
TMI–Control | 0.09 (0.03)** | 0.19 (0.07 to 0.31) | 0.12 (0.04)** | 0.23 (0.08 to 0.39) | 0.10 (0.04)** | 0.20 (0.05 to 0.36) | 0.09 (0.02)*** | 0.18 (0.08 to 0.28) | |
Combined–Control | na | na | 0.09 (0.04)* | 0.17 (0.02 to 0.32) | 0.08 (0.04)* | 0.16 (0.00 to 0.31) | 0.05 (0.03) | 0.10 (−0.01 to 0.21) | |
TPC–Combined | 0.07 (0.03)* | 0.15 (0.03 to 0.27) | 0.06 (0.04) | 0.12 (−0.03 to 0.28) | 0.09 (0.04)* | 0.17 (0.02 to 0.33) | 0.07 (0.02)** | 0.15 (0.05 to 0.25) | |
TMI–Combined | 0.09 (0.03)** | 0.19 (0.07 to 0.31) | 0.03 (0.04) | 0.06 (−0.09 to 0.21) | 0.02 (0.04) | 0.05 (−0.10 to 0.20) | 0.06 (0.02)* | 0.13 (0.03 to 0.22) | |
TPC–TMI | 0.02 (0.03) | 0.04 (−0.08 to 0.17) | 0.05 (0.04) | 0.09 (−0.06 to 0.25) | 0.08 (0.04)* | 0.15 (0.00 to 0.31) | 0.04 (0.02) | 0.08 (−0.02 to 0.18) | |
Treat–Controlb
| 0.08 (0.02)*** | 0.17 (0.09 to 0.24) | |||||||
Vegetables in grams per daye
| TPC–Control | 9.97 (4.22)* | 0.14 (0.02 to 0.26) | 29.81 (6.01)*** | 0.40 (0.24 to 0.56) | 19.51 (6.23)** | 0.25 (0.09 to 0.41) | 15.80 (3.65)*** | 0.21 (0.12 to 0.31) |
TMI–Control | 9.43 (4.24)* | 0.14 (0.02 to 0.26) | 10.45 (5.80) | 0.14 (−0.01 to 0.29) | 13.41 (6.06)* | 0.17 (0.02 to 0.33) | 9.11 (3.62)* | 0.12 (0.03 to 0.22) | |
Combined–Control | na | na | 14.28 (5.84)* | 0.19 (0.04 to 0.35) | 11.46 (6.05) | 0.15 (−0.01 to 0.30) | 8.29 (4.26) | 0.11 (0.00 to 0.23) | |
TPC–Combined | 9.97 (4.22)* | 0.14 (0.02 to 0.26) | 15.52 (5.90)** | 0.21 (0.05 to 0.36) | 8.05 (6.16) | 0.10 (−0.05 to 0.26) | 11.57 (3.61)** | 0.16 (0.06 to 0.25) | |
TMI–Combined | 9.43 (4.24)* | 0.14 (0.02 to 0.26) | −3.83 (5.71) | −0.05 (−0.20 to 0.10) | 1.95 (6.00) | 0.03 (−0.13 to 0.18) | 4.64 (3.59) | 0.06 (−0.03 to 0.16) | |
TPC–TMI | 4.49 (4.26) | 0.07 (−0.06 to 0.19) | 20.47 (5.77)*** | 0.27 (0.12 to 0.43) | 7.41 (6.03) | 0.10 (−0.06 to 0.25) | 8.94 (3.62)* | 0.12 (0.03 to 0.22) | |
Treat–Controlb
| 11.36 (2.83)*** | 0.15 (0.08 to 0.23) |
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-Equality of an intervention effect across time points. This was done by replacing in all group × time terms the three time dummies (weeks 25, 47, and 73) by a single indicator for time (post: 0 = baseline, 1 = else). This model simplification was tested with a likelihood ratio test.
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-Equality of the intervention effects (TPC = TMI = combined) at any given time point. This was done by replacing the three group indicators with a single indicator (treat: 0 = control group, 1 = TPC/TMI/combined). With a likelihood ratio test this model was compared to the preceding models.