Table 2. Between-group effect sizes and findings of the regression analysis.
| MD | [95% CI] | d | [95% CI] | t | p | |
|---|---|---|---|---|---|---|
| Primary endpoint | ||||||
| Pain interference (MPI) | 0.65 | [0.44; 0.86] | 0.69 | [0.46; 0.92] | 5.95 | <0.001 |
| Sensitivity analyses | ||||||
| Per-protocol analysis | 0.74 | [0.54; 0.94] | 0.79 | [0.58; 1.01] | 7.33 | <0.001 |
| Completer analysis | 0.56 | [0.37; 0.75] | 0.60 | [0.39; 0.80] | 5.75 | <0.001 |
| Analysis with reference-based imputation | 0.49 | [0.33; 0.66] | 0.53 | [0.35; 0.70] | − | <0.001 |
| Confirmatory secondary endpoints | ||||||
| Emotional functioning (PHQ-9) | 1.88 | [0.79; 2.98] | 0.40 | [0.17; 0.63] | 3.38 | 0.002* |
| Health-related quality of life (AQoL-8D) | −2.68 | [−4.66; −0.69] | −0.23 | [−0.40; −0.06] | −2.65 | 0.008* |
| Exploratory secondary endpoints | ||||||
| Pain experience (MPI) | ||||||
| Pain intensity | 0.29 | [0.07; 0.52] | 0.34 | [0.08; 0.61] | 2.56 | 0.011 |
| Life control | −0.08 | [−0.34; 0.17] | −0.08 | [−0.31; 0.16] | −0.63 | 0.527 |
| Affective distress | 0.29 | [0.04; 0.54] | 0.25 | [0.04; 0.47] | 2.31 | 0.021 |
| Pain intensity and interference (BPI) | ||||||
| Total scale | 0.73 | [0.34; 1.11] | 0.41 | [0.20; 0.63] | 3.74 | <0.001 |
| Pain interference with daily activities (PDI) | ||||||
| Total scale | 4.47 | [1.88; 7.06] | 0.34 | [0.14; 0.54] | 3.39 | <0.001 |
| Anxiety (GAD-7) | ||||||
| Total scale | 0.62 | [−0.25; 1.50] | 0.14 | [−0.05; 0.33] | 1.40 | 0.162 |
| Pain processing (FESV) | ||||||
| Action planning | −2.49 | [−3.37; −1.61] | −0.52 | [−0.70; −0.33] | −5.54 | <0.001 |
| Cognitive restructuring | −3.32 | [−4.30; −2.35] | −0.71 | [−0.92; −0.50] | −6.67 | <0.001 |
| Experience of competence | −2.15 | [−3.06; −1.23] | −0.49 | [−0.70; −0.28] | −4.61 | <0.001 |
| Mental distraction | −1.08 | [−1.92; −0.24] | −0.28 | [−0.49;−0.06] | −2.54 | 0.011 |
| Counteracting activities | −0.57 | [−1.42; 0.28] | −0.14 | [−0.34; 0.07] | −1.31 | 0.189 |
| Relaxation techniques | −3.32 | [−4.31; −2.32] | −0.70 | [−0.91; −0.49] | −6.54 | <0.001 |
| Pain-related helplessness and depression | 2.31 | [1.01; 3.60] | 0.37 | [0.16; 0.58] | 3.50 | <0.001 |
| Pain-related anxiety | 1.98 | [0.95; 3.01] | 0.38 | [0.18; 0.57] | 3.77 | <0.001 |
| Pain-related anger | 1.46 | [0.16; 2.76] | 0.22 | [0.02; 0.41] | 2.20 | 0.028 |
| Pain acceptance (CPAQ) | ||||||
| Total scale | −8.22 | [−11.34; −5.11] | −0.49 | [−0.68; −0.31] | −5.19 | <0.001 |
| Activity willingness | −4.96 | [−7.01; −2.90] | −0.47 | [−0.66; −0.27] | −4.74 | <0.001 |
| Pain willingness | −3.23 | [−4.84; −1.62] | −0.37 | [−0.56; −0.19] | −3.93 | <0.001 |
| Psychological flexibility (AAQ-II) | ||||||
| Total scale | 2.86 | [1.34; 4.38] | 0.30 | [0.14; 0.46] | 3.69 | <0.001 |
| Psychological flexibility (PIPS) | ||||||
| Total scale | 6.14 | [3.83; 8.44] | 0.54 | [0.34; 0.75] | 5.24 | <0.001 |
| Pain avoidance | 4.08 | [2.32; 5.83] | 0.47 | [0.27; 0.67] | 4.57 | <0.001 |
| Cognitive fusion with pain | 2.06 | [1.15; 2.96] | 0.49 | [0.27; 0.70] | 4.46 | <0.001 |
| Pain-specific self-efficacy (PSEQ) | ||||||
| Total scale | −5.51 | [−7.89; −3.13] | −0.44 | [−0.63; −0.25] | −4.55 | <0.001 |
p-values are adjusted for multiple testing (Holm-Bonferroni correction)
For the following instruments, higher values indicate a better outcome, and thus negative mean differences/effect sizes indicate a better expression of the endpoint in the i ntervention group compared to the control group: AQoL-8D, subscale of MPI (life control), subscales of FESV (action-planning competencies, cognitive restructuring, experience of competence, mental distraction, counteracting activities, rest and relaxation techniques), CPAQ, PSEQ. As is common in studies on digital psychological interventions, women were overrepresented in the sample (85.8%), potentially limiting the generalizability of the results to men. MD, mean difference; CI, confidence interval; d, Cohen’s d; MPI, Multidimensional Pain Inventory; PHQ-9, Patient Health Questionnaire-9; AQoL-8D, Assessment of Quality of Life 8-Dimension; BPI, Brief Pain Inventory; PDI, Pain Disability Index; GAD-7, Generalized Anxiety Disorder Scale-7; FESV, German Pain Processing Questionnaire; CPAQ, Chronic Pain Acceptance Questionnaire; AAQ-II, Acceptance and Action Questionnaire-II (German version); PIPS, Psychological Inflexibility in Pain Scale; PSEQ, Pain Self-Efficacy Questionnaire