Soler 2009.

Study characteristics
Methods	design: parallel‐arm, randomised controlled trial
Participants	sex: 48/59 females (81.3%) age: mean age 29.2 years location: Spain setting: outpatient exclusions: schizophrenia, drug‐induced psychosis, organic brain syndrome, alcohol or other psychoactive substance dependence, bipolar disorder, mental retardation, major depressive episode in course, CGI‐S score ≤ 4 (i.e. not at all, borderline, or mildly ill) level of functioning/severity of illness: mean CGI‐BPD (global) scores of both groups: group 1: 4.71; range 4‐7; group 2: 4.9, range 4‐7; i.e. mean severity was moderately to markedly ill BPD diagnosis according to: DSM‐IV means of assessment: SCID‐II, DIB‐R
Interventions	group 1 (EG): DBT skills training (DBT‐ST), including DBT original skills for interpersonal effectiveness, emotional regulation, mindfulness and distress tolerance; 13 psychotherapy sessions of 120 min each, conducted by 2 therapists (a male and a female) for each group, in groups of 9‐11 participants. group 2 (CG): Standard Group Therapy (SGT); therapeutic techniques: interpretation, highlighting, exploration, clarification, confrontation; therapists targeted specially nihilistic or destructive interactions, characteristic BPD interactions and those that could interfere with group functioning; 13 psychotherapy sessions of 120 min each, conducted by 2 therapists (a male and a female) for each group, in groups of 9‐11 participants. duration: 3 months (i.e. 13 weekly sessions in each condition) concomitant psychotherapy: participants did not receive any other individual or group psychotherapy concomitant pharmacotherapy: pharmacological therapy was continued if initiated prior to inclusion, but type and doses could not be modified during the study period
Outcomes	outcomes considered in this review self‐rated: mental health status (CGI‐I‐self rating) observer‐rated: BPD severity (CBI‐BPD‐global), anger (CBI‐BPD‐anger), affective instability (CGI‐BPD‐affective instability), chronic feelings of emptiness ((CGI‐BPD‐emptiness), impulsivity (CGI‐BPD‐impulsivity), suicidality (CGI‐BPD‐suicidality), interpersonal problems (CGI‐BPD‐unstable relations), dissociative/psychotic pathology (BPRS), depression (Ham‐D‐17), anxiety (HARS), general psychopathology (SCL‐90‐R‐GSI) time‐points used here: 3 months, i.e. post‐treatment
Notes	analyses: ITT
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Blocks of four generated using the SPSS software program served for the randomisation to DBT‐ST or SGT." (Soler 2009, p. 354)
Allocation concealment (selection bias)	Unclear risk	No further details. Comprehensible flow diagram of patient progress through phases of study provided.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"... participants were evaluated every two weeks by experienced psychiatrists. Subjects were instructed not to disclose any information about the group (topics, group members or therapists) to maintain blind conditions." (Soler 2009, p. 354) "Assessment and drug control were carried out by two psychiatrists who were masked to the experimental conditions." (Soler 2009, p. 355) "We are unable to affirm that all participants refrained from disclosing information about the therapy or the therapists with the psychiatric raters during assessment visits. [...] Indeed, the observer‐rater scales obtained during the interview visits and the results from self‐reported measures filled in by patients during the study showed a good concordance. " (Soler 2009, p.357)
Selective reporting (reporting bias)	Unclear risk	No indication for selective reporting, but Insufficient information to permit judgement of 'Yes' or 'No'.
Treatment adherence?	Unclear risk	"DBT‐ST intervention was led by two cognitive behavioural psychotherapists with prior experience in BPD group therapy (Soler et al., 2001, 2005) and trained in DBT in courses organised by the 'Behavioural Technology Transfer Group'." (Soler 2009, p. 355).
Allegiance effect improbable?	Low risk	No indications for allegiance effect given.
Attention bias: equal amounts of attention to all groups (obligatory treatment components)?	Low risk	Equal amounts of attention spent to both groups.