Table 2.
Study characteristics
| Study | Sample/eligibility | Conditions | Support | Intervention | Follow-up period (rate) | Outcome | Conclusions | Quality assessment |
|---|---|---|---|---|---|---|---|---|
| Buntrock et al. [41, 42] |
N = 406; German general pop. (no MDD on SCID). Aged 18+ years (73.9% female) |
i. iCBT ii. Psychoed. |
Automated SMS reminders, 2 h online trainer feedback | 6 × 30 min sessions (3–6 weeks). Behavioural and problem-solving therapy. | 6 weeks (90.1%) 6 months (80.0%) 12 months (82.3%) Mean sessions: 5.84 |
Symptom reduction (CES-D). MDD incidence. | 6-week BG ES: Cohen’s d = 0.69 (F1,403 = 54.104, p < .001). 6-month BG ES: Cohen’s d = 0.28 (F1,402 = 9.240, p = .003). There was a significant difference in MDD incidence rates over 12 months favouring the intervention group (hazard ratio = 0.59, 95% CI: 0.42–0.82; p = .002). |
23 |
| Christensen et al. [43] |
N = 558; Australian Internet users (No anxiety disorder on MINI). Aged 18–30 years (80.6% female) |
i. iCBT + Psychoed. (A) ii. A + telephone reminders iii. A + email reminders iv. Placebo website (B) v. B + telephone reminders |
Differing reminder conditions, 2-min/week. No therapeutic content. | 10 × 10 weekly sessions. Mindfulness-focussed CBT for anxiety (e-couch). | 10 weeks (64.5%) 6 months (54.3%) 12 months (47.3%) Mean sessions: (i) 3.7; (ii) 7.3; (iii) 5.5; (iv) 3.7; (v) 8.3. |
Symptom reduction (GAD-7). GAD incidence. |
Significant time effects for each of the three follow-ups. No significant group × time effects for any comparison. Overall, indicated prevention of GAD was deemed not effective | 21 |
| Clarke et al. [46] | Relevant subgroup: n = 63; US HMO member adults (CES-D < 20). Aged 18+ years (75.6% female) |
i. iCBT + Psychoed. ii. Usual care |
No support. | 7 chapters. CBT skills program (focusing on the cognitive restructuring techniques). | 4 weeks (52.8%) 8 weeks (65.2%) 16 weeks (65.5%) 32 weeks (59.2%) Mean logins: 2.6 |
Symptom reduction (CES-D). | Significant reduction in symptoms in intervention participants compared to control at the 16-week (BG ES: Cohen’s d = 0.17, p < .05) and 32-week (BG ES: Cohen’s d = 0.48, p < .01) follow-up. | 16 |
| Cukrowicz et al. [47] |
N = 152; US undergrad. (BAI ≤ 18; BDI ≤ 19). 95% aged 18–21 years (73.7% female) |
i. Psychoed. + CBT ii. Psychoed. |
Facilitated session. | 6 × 20 min segments (1 laboratory session). Situational analysis-focussed CBT. |
2 months (90.3%) | Symptom reduction (BAI & BDI). | BAI, BG ES: Cohen’s d = 0.24 (F1,145 = 7.84, p < .01). BDI, BG ES: Cohen’s d = 0.27 (F1,145 = 9.64, p < .01. Additional significant reductions on PANAS and STAI-S, and Reliable Change Index. |
17 |
| Imamura [44, 52] | N = 762; Japanese workers (No past month MDD on WHO-CIDI). Aged 18+ years (16.1% female) |
i. iCBT ii. Stress reduction tips email |
Email reminders. Homework feedback from clinical psychologist. | 6 × 30 min sessions (6 weeks). CBT skills program (self-monitoring, cognitive restructuring, assertiveness, problem solving, and relaxation). | 3 months (79.5%) 6 months (77.7%) 12 months (67.1%) Mean sessions: 4.53 |
Symptom reduction (BDI-II). MDE incidence. | 3-month BG ES: Cohen’s d = −0.14, 95% CI: −0.30 to 0.02 (t 621.35 = − 1.99, p < .05). 6-month BG ES: Cohen’s d = −0.16, 95% CI: −0.32 to 0.00 (t 621.35 = − 1.99, p < .05). 12-month BG ES: Cohen’s d = −0.08, 95% CI: −0.26 to 0.09 (t 610.33 = − 1.42, p = .16). Significant reduction in MDE incidence in intervention compared to control at 12-month (Log-rank χ 2 = 7.04, p < .01) but not 6-month (Log-rank χ 2 = 3.26, p = .07). |
24 |
| Levin et al. [48] | Relevant subgroup: n = 43; US undergrad. (DASS in normal range). Aged 18–21 years (53.9% female) |
i. ACT ii. Waitlist |
Email reminders. | 2 sessions. Youth-focussed ACT program. | 3 weeks (79.5%) 6 weeks (77.7%)a 92% completed program |
Symptom reduction (DASS). | No significant between group differences were observed on depression, anxiety of stress among the non-distressed subgroup (p > .10). | 19 |
| Lintvedt et al. [49] | Relevant subgroup: n = 52; Norwegian undergrad. (subclinical: CES-D). Aged 18+ years (53.9% female) |
i. Psychoed. + iCBT ii. Waitlist |
Weekly automated assignments. | 5 weekly modules. CBT, interpersonal therapy, relaxation self-help program (Moodgym) & psychoed. Program (Bluepages) | 8 weeks (68.0%) Mean modules: 2–3 |
Symptom reduction (CES-D). | There was a significant increase in depressive symptoms for the subclinical control group compared to the intervention group (F 1,24 = 6.86, p < .05; Hedges g = 0.61). | 22 |
| Morgan et al. [50] |
N = 1326; English speaking gen. Pop. (subclinical: PHQ-9) Aged 18–79 years (77.6% female) |
i. Self-help emails ii. Psychoed. emails |
No support. | 2 emails/week (6 weeks). Persuasive framing, tailoring, goal setting, limiting cognitive load. | 3 weeks (54.8%) 6 weeks (42.9%) 95.6% received the emails |
Symptom reduction (PHQ-9). | There was a small significant difference in depression symptoms in intervention group compared to control (d = 0.17, 95% CI: 0.01 to 0.34). There was a lower, although non-significant, risk of major depression in the active group. | 20 |
| Musiat et al. [51] | Relevant subgroup: n = 859; UK tertiary students (low risk on the SURPS). Aged 18–57 years (70.5% female) |
i. iCBT ii. Student life program |
No support. | 5 × 30 min modules Personality trait-driven CBT program (PLUS) | 6 weeks (49.7%)a
12 weeks (38.3%) 47% completed a module |
Symptom reduction (PHQ-9; GAD-7). | Significant intervention effects were found in the high risk group but for those at low risk no significant change was detected in PHQ-9 (p > .999) or GAD-7 (p = .415) | 21 |
| Spek et al. [40, 45] |
N = 301; Dutch older general pop. (no MDD on WHO-CIDI). Aged 50–75 years (63.5% female) |
i. iCBT ii. group CBT iii waitlist |
No support. | 8 sessions (8 weeks) Psychoed. and CBT (Coping with depression) | 10 weeks (60.1%) 12 months (63.1%) Mean modules: 5.5 |
Symptom reduction (BDI-II). | Significant intervention effects were found in both intervention groups compared to control. No differences were found between interventions (Internet vs control: post-treatment BG ES: Cohen’s d = 0.55; 12-month BG ES: Cohen’s d = 0.53). | 24 |
MDD major depressive disorder, MDE major depressive episode, Psychoed. psychoeducation, iCBT Internet Cognitive Behavioural Therapy, SCID Structured Clinical Interview for DSM, TAU treatment as usual, MINI Mini-International Neuropsychiatric Interview, HMO Health Maintenance Organization, BDI-II Beck Depression Inventory, BAI Beck Anxiety Inventory, WHO-CIDI World Health Organisation Composite International Diagnostic Interview, PHQ-9 Patient Health Questionnaire, GAD-7 Generalized Anxiety Disorder–7-item scale, BG ES between-group effect size, ACT Acceptance and Commitment Therapy, CES-D Center for Epidemiological Studies-Depression, DASS Depression Anxiety Stress Scale; undergrad. Undergraduate, PANAS Positive and Negative Affect Schedule, STAI-S State-Trait Anxiety Inventory
aResults not reported at this follow-up point