Using the ALSPAC dataset, this study will address the following questions:

Study 1

* Aim: Are there individual-level associations between parental income, occupation, education and single-parent status and risk of ADHD in the child? Hypothesis: all the above factors will be independently negatively associated with an outcome of ADHD. Exposure variables: parental income, occupation, education and marital status near birth-age 3 of child. Outcome: ADHD by DAWBA at age 7 1/2 (no confounding variables in this study).

* Aim: Which socioeconomic association is strongest, and what are the potential mechanisms for this effect? For example, if single parenthood is the most salient factor, is this due to mediation by poor diet, mothers' smoking during pregnancy, or other factors? Hypothesis: using the strongest predictor above, this association will be mediated by parenting/diet/smoking. Exposure variables: SES variable. Confounding/moderating/mediating variables: diet at age 3, caffeine intake at 6/7 years old, parent involvement, parent mental health. Outcome variable: ADHD by DAWBA at age 7.

Study 2

* Aim: Does this association vary by ADHD at developmental stage or by change in family SES? Hypothesis: SES variables measured at birth/infancy will be the strongest predictors of ADHD at age 7 or 15. Change in family SES will be associated with a change in ADHD symptoms as measured by the SDQ.

Exposure variables: SES variables at several timepoints. Confounding variables: Significant confounders from study 1 part 2. Outcome variables: ADHD by DAWBA and attention symptoms on SDQ at age 7, 9, 11, 15.

Study 3

* Aim: What is/are the most salient measure/s SES when evaluating risk of ADHD in children? (parent SES factor vs school-level factors added to model) This study has implications for policy with regards to early intervention to reduce prevalence of ADHD, as well as contributing to health inequalities literature and also moving toward suggesting a standardised or single SES measure to be used in future research, reducing heterogeneity within the research community. Hypothesis: single parent status, income and school-level deprivation will be the strongest predictors of ADHD outcome. Exposure variables: Parental income/education/occupation/single parenthood, school-level deprivation (free school meal status or IMD), and class-level deprivation (number of free school meals in class). Outcome variables: ADHD by DAWBA at age 7 and 15.