Box 1. Child, family, school and area variables assessed.

Exposure of interest	Ethnicity
	[P] Indian vs. White
A priori confounders	[P] Child’s age
	[P*] Child’s gender
	[I] Survey year (1999 vs. 2004)
Level 1: area characteristics, school characteristics and family SEP	Area characteristics
	[I] Geographical region: North East; North West; Yorkshire & Humberside; East Midlands; West Midlands; East Anglia; London; South East; South West.
	[I] Metropolitan vs. non-metropolitan region
	[I*] Small area deprivation, from the 2004 English Indices of Multiple Deprivation (Noble, et al., 2004).
	School characteristics
	[I*] Ford Score, a predictor of the prevalence of mental health problems in a school (A. Goodman & Ford, 2008).
	Family SEP
	[P] Responding parent’s highest educational qualification: no qualifications [coded 1]; poor GCSEs (grades D-F) or equivalent [2]; good GCSEs (grades A-C) [3]; A-level [4]; diploma [5]; degree [6].
	[P] Weekly household income: £0-99 [coded 0.5]; £100-199 [1.5]; £200-299 [2.5]; £300- 399 [3.5]; £400-499 [4.5]; £500-599 [5.5]; £600-769 [6.85]; £770 or over [8.5].
	[P] Housing tenure: owner occupied; social sector rented; privately rented.
	[P] Occupational social class: I; II; III Non-manual; III Manual; IV; V; Never worked; Full- time student.†
	[P] Mother’s economic activity: full time employed; part-time employed; looking after home and family; unemployed; other.
	[P] Father’s economic activity: as for mother’s economic activity
Level 2: Family composition and family stress	Family composition
	[P] Family type: two-parent; stepfamily; lone parent family
	[P] Parents married vs. cohabiting
	[P] Three-generation household: grandparent present vs. no grandparent present
	[P] Number of co-resident siblings
	[P*] Mother’s age at child’s birth
	Family stress
	[P*] Parent’s mental health, from the 12-item General Health Questionnaire (GHQ-12: Goldberg & Williams, 1998).†
	[P*] Family functioning, from the general functioning subscale of the McMaster Family Activity Device (Miller, Epstein, Bishop, & Keitner, 1985).†
	[P] Family ever experienced parental separation : yes/no
	[P] Family ever experienced financial crisis: yes/no
	[P] Family member (not the child) ever had police contact: yes/no
	[P] Family ever experienced the death of a parent or sibling of the child: yes/no
Level 3: Child characteristics	Physical disorders†
	[P] Neuro-developmental disorder: yes/no
	[P] Developmental problems or immaturity: yes/no
	[P] Common physical health disorder: yes/no
	[P] Rare physical health disorder: yes/no
	Stressful life events to child
	[P] Child ever experienced serious illness requiring hospitalisation: yes/no
	[P] Child ever experienced death of a friend: yes/no
	Substance use†
	[C] Regular smoking (≥1 cigarette a week): yes/no.
	[C] Frequency of alcohol consumption: less than once a fortnight; once a fortnight to once a week; twice a week or more.
	[C] Ever used illegal drugs: yes/no
	Academic abilities and difficulties
	[T*] Teacher-reported academic difficulties (range 0-9), created by summing the teacher’s response to question on the child’s ability in 1) maths, 2) reading 3) spelling. Each question had response options above average [coded 0]; average [1]; some difficulty [2]; or marked difficulty [3].
	[P] Parent-reported learning difficulties: yes/no
	[P] Parent-reported dyslexia: yes/no
	[A*] Formal tests of reading ability, from the British Ability Scales, second edition (Elliott, Smith, & McCulloch, 1996); B-CAMHS 1999 only
	[A*] Formal tests of spelling ability, measured as for reading ability; B-CAMHS 1999 only
	Parent reward and punishment behaviours; B-CAMHS 1999 only
	[P] Frequency of praising child: never; seldom; sometimes; often.
	[P] Frequency of non-physical punishment: never; seldom; sometimes; often.
	[P] Frequency of smacking child: never; seldom; sometimes; often.
	[P] Ever hits or shakes the child: yes/no
	Relationships with relatives; B-CAMHS 2004, 11-16 year olds only
	[C*] Perceived social support (range 0-14), using seven questions from the 1985 Health and Lifestyle Survey (Cox, et al., 1987).†
	[C] Number of close relatives inside the home
	[C] Number of close relatives outside the home
	[C] How often child helps relatives: under once a month; once a month; once a week; daily.
Outcomes	Externalising problems
	[P] Parent externalising SDQ score
	[T] Teacher externalising SDQ score

[P]=parent-reported; [T]=teacher-reported; [C]=child-reported; [A]=formal assessment; [I]=investigator-assigned.

^*=continuous variables.

^†=Further information in Electronic Appendix