Strengths and limitations
fatigue, pain
STILL
Notably, this study has some strengths that are rarely seen in RCTs examining the effects of psychological interventions. The inclusion of a carefully matched non-specific control condition and a no-treatment control in a 3-armed RCT together with the attempt to reduce significant threats to internal validity (e.g., balancing therapist training, adherence, and competence; controlling for therapist effects; ensuring an equal treatment structure across conditions; and balancing non-specific factors) entails that the findings of this study may be highly robust.According to the power analysis we needed 81 participants to be able to detect significant differences in the primary outcome. Despite a smaller sample size, significant differences were found between the groups for the primary outcome While the small sample size would contribute considerably to the risk of type 2 error, one should also bear in mind that a large number of statistical tests were performed in the study, and hence there is considerable risk of type 1 error. Still, some interesting significant pre-post changes were found in our data including increased workability and lower fatigue in the MY-ENDO group. However, these effects did not show statistically significant differences between the groups, and larger sample sizes are needed in future studies to answer questions about specificity.Recruiting participants was difficult due to patients suffering from physical disabilities and lack of energy making the 3-h in-person commitment a barrier to participation. Other barriers were geographical distance and working schedules.Future studies could try new ways to overcome these limitations for example by stratifying participants by use of pain medication and offering digitally delivered therapy to this patient group.