Aim :To establish whether cigarette smoking causally influences risk of depression, self-harm and suicide

We will use rs1051730 / rs16966968 as a genetic instrumental variable to establish whether cigarette smoking causes depression, self-harm and suicide.

We hypothesise that the risk allele for heavy smoking will be associated with increased depression and it's sequelae, that this association will be fully accounted for by cigarette smoking, and that this association will not be observed in non-smokers.

Aims: To investigate whether the contribution of cigarette smoking to depression varies with age.

Based on evidence from preclinical studies relating to the sensitivity of the adolescent brain to nicotine, we hypothesise that cigarette smoking increases the risk of depression, and that this risk is greater in adolescence than adulthood.

To investigate the use of linkage of administrative data to corroborate outcome status.

Where available, we will use linked administrative data (e.g., electronic patient records, Hospital Episodes Statistics database) to corroborate outcome / exposure status, and explore whether classifications based on these influence apparent effects of exposure.