Table 2 List of study outcome measures

Primary outcome measure: Child Behaviour Checklist (CBCL)

Each question relates to a specific behaviour and is measured on a 3-point Likert Scale. Overall scores are derived for behavioural difficulties, attention problems and aggression. A T-score of Total Problem Behaviours of 60 or over signifies borderline to clinical caseness. CBCL incorporates DSM-5 diagnostic categories which rate comorbidities, e.g. autism spectrum disorders, mood disorders.

Mullen Scales of Early Learning

Assesses child level of disability [26]. Only assessed during the baseline assessment.

Revised Family Observation Schedule (FOS-RIII)

FOS-RIII is an objective measure of parent-child interaction, previously used in studies investigating SSTP and codes 20 min (four 5-min consecutive sections) home based videotaped parent-child interactions [27]. There will be an inter-rater reliability exercise on a proportion of the observations to ensure reliability.

Child Behaviour Checklist Caregiver-Teacher Report Forms (C-TRF)

Most children in the sample age range will have additional care outside the parental home allowing us to have additional perspectives on the child’s behaviour. The CBCL and C-TRF are extensively used to measure child’s behaviour and there are positive reports about high completion rates by teachers/nursery staff as shown in other studies [28].

General Health Questionnaire (GHQ)

Common psychiatric morbidity in the parent will be assessed at baseline, 4-month and 12-month follow-up.

Questionnaire on Resources and Stress (QRS-F short form)

Measures parental stress in caregivers of chronically ill or children with ID at baseline, 4-month and 12-month follow-up [29].

Caregiving Problem Checklist-Difficult Child Behaviour

The frequency of difficult child behaviour when the parent is completing care-giving tasks will be measured at baseline, 4-month and 12-month follow-up. Internal consistency is adequate (α = .78) [30].

Parenting Sense of Competence Scale (PSOC)

Assesses Satisfaction and Efficacy competencies as a parent at baseline, 4-month and 12-month follow-up [31]. Internal consistency for the measure ranges from α = .70–.80 [31].

Child and Adolescent Service Use Schedule (CA-SUS)

A modified version will be used in the trial to assess child health and social care service use at baseline, 4-month and 12-month follow-up [32].

Paediatric Quality of Life (PedsQL)

Assesses health related quality of life. The measure covers Physical, Emotional, Social, and School Functioning domains. It contains a parent proxy report for children aged 2 years and over and will be used in the study to derive Quality-Adjusted Life Year (QALYS) for the health economic evaluation. Internal consistency for the parent version is acceptable (α = .86) and has demonstrat4ed discriminant validity. This will be completed at baseline, 4-month and 12-month follow-up [33].

EuroQol-5D

Captures parental and caregiver perspective on their health status at baseline, 4-month and 12-month follow-up which will be used in the economic evaluation [34].

Client Satisfaction Questionnaire

Measures parent intervention acceptability [35]. The questionnaire will allow parents to provide feedback about the intervention during the 4 month follow-up by commenting on their satisfaction with and experience of the intervention, including ease of use, format and helpfulness. It has been specifically developed for research in SSTP and has high internal consistency (α = .92) [30].

Case Report Forms (CRF)

To collect sociodemographic and clinical information about comorbidities.