Eight RCTs (text reported 1,093 patients, table reported 1,369; range 58 to 405) were included in the review. One RCT met all quality criteria and was considered to be at low risk of bias. Two studies reported adequate methods of randomisation and allocation concealment. Six studies reported adequate blinding. Five studies adequately addressed incomplete outcome data. Seven studies were considered to be free of selective reporting. The attrition rate ranged from 5.2 to 21%.
Overall, telephone-delivered cognitive behavioural therapy significantly improved physical health in patients with chronic illnesses (d=0.225, 95% CI 0.105 to 0.344, eight RCTs). There was high statistical heterogeneity (Ι²=78%).
Subgroup analysis found that studies that included less than five hours of therapist contact had a greater impact on health outcomes than those with more than five hours therapist contact. Moderator analysis found no significant differences between interventions focused mainly on emotions and those which focused mainly on physical illness. There was no significant effect of treatment for studies that aimed to improve immediately life-threatening illnesses. However for studies focusing on less serious illnesses, the effect remained significant (d=0.346, 95% CI 0.172 to 0.520).
Analysis of publication bias reported that 36 unpublished, non-significant studies of the effect of the intervention on physical health would be needed to make the overall result non-significant.