Gross 2009.

Methods	Cluster randomised controlled trial.
Participants	Participants: parents or legal guardians of a 2‐4 year old child enrolled at the day care participating centre. Sex: 225 mothers, 17 fathers, 4 foster parent, 5 grandparents, and 2 other (sex of participants reported only on 253 participants who were included in analysis). Age of parents: not stated. Unit of allocation: a day care centre. Number randomised: 7 day centres (3 intervention; 4 control); 292 participants (156 intervention; 136 control). Number used in analysis: 7 day centres (3 intervention; 4 control); 253 participants (135 intervention; 118 control); number used in analysis for the 'depressive symptoms', 'stress' and 'confidence' outcomes: 247 (133 intervention; 114 control). Country & setting: USA; multi‐site (n=7); recruited from community settings; intervention delivered in the community. Inclusion criteria: Day care centre: had over 90% of enrolled families meeting income‐eligibility requirements for subsidised child care; was licensed by the Dept of Child and Family Services; provided full‐day child care; enrolled at least 60 children in the target age group; had a space on site to run a weekly parent group, and the director was willing to allow the site to be randomised. Participant: a parent or a legal guardian of a 2 to 4 year old child (if more than one in this age range, the youngest child was selected for inclusion); should speak English. Exclusion criteria: not stated. Ethnicity: 149 African‐American, 83 Latino, 12 white (not Latino), 9 other (intervention group had more Latino parents than control group, P<0.01). Baseline characteristics: There were no differences between two groups on parent age, educational level, employment status, marital status, or child age; there were significant differences between these two groups on parent/race ethnicity and child gender.
Interventions	Two conditions: Webster‐Stratton parent programme; wait‐list control. Duration of intervention: 12 weeks. Length of follow‐up: 6 months; 12 months.
Outcomes	Depressive symptoms (Center for Epidemiological Studies Depression Scale). Stress (Everyday Stress Index). Confidence (Toddler Care Questionnaire).
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Trial investigators report “The day care centres were matched on size, racial/ethnic composition, percentage single‐parent households, and median income and randomly assigned to an intervention or control condition” (page 56). Information reported insufficient for a judgment to be made, but information from trial investigator (email from D Gross to CB on 11 Oct 2010) indicates that a random numbers table was used.
Allocation concealment (selection bias)	High risk	Information reported insufficient for a judgment to be made, but information from trial investigator (email from D Gross to CB on 11 Oct 2010) indicates that sealed opaque envelopes were not used.
Blinding (performance bias and detection bias) Participants	High risk	Review authors judge that it would not be possible to fully blind participants in this type of study, and found no indication of any specific additional measures taken to reduce the risk of bias that might result from differential behaviours by participants.
Blinding (performance bias and detection bias) Personnel	High risk	Information reported insufficient for a judgment to be made, but information from trial investigator (email from D Gross to CB on 11 Oct 2010) stated that "the research assistant collecting the surveys from parents could not be blinded".
Blinding (performance bias and detection bias) Outcome assessors	Unclear risk	Information from trial investigator (email from D Gross to CB on 11 Oct 2010) indicated that "the DPICS coders were blinded”.  However, no information for parent self‐report measures.  Information reported insufficient for a judgment to be made
Incomplete outcome data (attrition bias) All outcomes	Low risk	The trial investigators report that “Thirty nine (13%) participants dropped out of the study before their 1 year follow‐up.  Attrition in the control condition was attributed to 17 parents (12.5%) who were lost to follow‐up and 1 parent (0.7%) who withdrew.  Attrition in the intervention condition was attributed to 11 parents (7.1%) lost to follow‐up, 9 parents who withdrew, and 1 parents (5.8%) who withdrew, and 1 parent who was dropped from the study due to emotional problems that interfered with her ability to participate in group discussion” (page 59). For ‘depressive symptoms’, ‘stress’ and ‘confidence’ outcomes 23/156 participants (14.7%) dropped out from treatment group and 18/136 participants dropped out from the control group (13.2%).  Review authors considered the numbers of and reasons for missing data reasonably likely to be balanced across the treatment conditions. Overall attrition was 14%.
Selective reporting (reporting bias)	High risk	The three outcomes, ‘depressive symptoms’ (CESD), ‘stress’ (ESI) and ‘confidence’ (TCQ) were not pre‐specified, nor reported, although they were measured. The authors provided the data (email from D Gross to CB on 27/12/10) stated “We did not include them in the 2009 paper because of (1) length and (2) their lack of association with the outcome variables, and therefore, did not contribute to the results”.
Other bias	Low risk	Trial investigators report “There were significant differences between intervention and control parents on parent race/ethnicity and child gender. To control for baseline differences, these variables were included as co‐variates in the analytic models (page 56). The study appears to be free of other sources of bias.