Twenty two RCTs of computerised CBT for major depression, social phobia, panic disorder or generalized anxiety disorder showed superiority in outcome over control groups. The effect sizes are substantial, and the results indicate both short term and long term benefits. Furthermore, patients adhered to and were satisfied with computerised CBT, despite the significantly reduced amount of contact with the clinician. Thus, computerised CBT is an efficacious and acceptable treatment, and by increasing convenience and reducing clinician time that would otherwise be required by face-to-face treatment, it offers increased access to treatment for those suffering from anxiety and depression.
The results come from 9 different groups working independently in 7 different countries. Similar results were obtained for each disorder and heterogeneity was non-significant for each disorder and for all studies together. It is as though there is a core set of CBT skills that is of benefit in the internalising disorders included in this analysis.
Most patients had been recruited as volunteers, largely after media publicity, but a minority were referred by their clinician. This raises the question, ‘are these patients comparable to patients who seek face-to-face treatment?’ In a large study (n
774), internet patients with one of these four disorders were as severe when assessed by symptom, distress and disability measures as those attending a face-to-face clinic, and both groups were significantly more severe than cases identified in an epidemiological survey 
. Another index of severity is treatment history. Three studies reported this. In one study of iCBT for depression in a primary care setting, three quarters of patients had a history of previous episodes 
. The chronicity was similar in two iCBT studies for depression in community volunteers. In the first 
70% had sought prior help and 51% were currently taking medication for their depression. In the second study 
help seeking and medication rates were comparable and 72% said their onset of depression was before the age of 21, 78% said they had had more than 5 episodes and 78% said that they had had no remission in the last 2 years. Thus, it appears that participants in these trials resemble people who attend regular clinics. There were few data on treatment history in the studies of anxiety disorders.
The mean effect size, indicating the superiority of the computerized intervention over the control group, was 0.88, NNT 2.15. The most common control group was waitlist, with treatment for them delayed until the intervention group had completed treatment. Placebo or active treatment control groups are preferable, but are difficult to arrange when there is no face to face contact with the participants. Interventions compared to waitlist controls have shown increased effect sizes compared to interventions compared to the treatment as usual studies 
and the null finding in the present meta-analysis may be due to insufficient power. There were no studies comparing computerised CBT and medication. Five studies compared internet therapy directly with face-to-face CBT for depression or panic disorder, and while all found strong pre-post treatment effects, none found differences between the two modes of delivery. We conclude that computerized CBT, with clinician or technician assistance which can be as brief as one hour per patient, can work as well as face-to-face CBT.
Adherence to computerized CBT was good; in the median study, 80% of individuals who began these programs completed all stages. This rate of completion suggests that computerized CBT was well accepted by participants. The programs contained between five and nine ‘lessons’. Conceivably, some participants who do not complete all the lessons may have gained all they need from the program. More research is needed regarding the tailoring of computerized programs to the needs of individuals. Ten of the 22 studies provided data on patient satisfaction; in the median study 86% of patients were satisfied or very satisfied with the computerized CBT program. Participants noted the advantages of computerized therapy, including convenience (such as completion of the program in the evening when there are no competing demands), ability to proceed at one's own pace to master the material, low cost and privacy. We conclude that computerised CBT is acceptable to patients.
There is a need for more extensive follow-up assessment as only 14 of the 22 studies provided follow-up data, at a median 26 weeks (range 4–52). As with face-to-face CBT 
, the benefits lasted and no significant relapse was reported.
The majority of studies identified measures of distress, disability, quality of life, or work force participation as secondary outcome measures. While changes in these secondary outcome measures were not as large as in the primary outcome measures, they were significant and demonstrate that internet treatment has the capacity to change health status not merely reduce specific symptoms. One study pooled data from three RCTs of social phobia and showed significant improvements in comorbid symptoms of depression and generalized anxiety even though the treatment was focused solely on the social phobia 
The benefits described are substantial yet the content of the programs is relatively simple and the therapist or technician contact brief. For example in the Andersson 
0.87), the treatment group had access to five weekly text ‘lessons’ about recovering from depression – behavioural activation, cognitive restructuring, sleep and physical health, and relapse prevention and future goals. This raises an issue of whether we presently conceptualise the nature of these four disorders correctly, either as related to temperament 
or to neurotransmitter abnormalities 
neither of which could be expected to yield to relatively brief sessions of skills based teaching about controlling worrying thoughts and confronting feared situations. The mechanism by which these programs produce benefit needs to be explored.
In sum, the 22 identified computerized CBT programs generated a large effect size superiority over control groups with maintenance of gains at follow-up and good patient adherence and satisfaction. As the programs become more sophisticated, the clinician or technician time required seems to be decreasing to the order of 10 minutes per week per patient 
Is it possible to integrate these internet services with existing mental health services so that people who do not recover with internet therapy can, in a stepped care design, receive face to face care? We now, it seems, are beginning to know enough about the efficacy, applicability and potential cost savings from the internet programs for people with anxiety and depressive disorders to begin to integrate these internet services with existing mental health services.