Table 3.

Exposure and outcome sample sizes and reported inverse variance weighted Mendelian randomisation estimates (odds ratio and 95%confidence interval) for the effect of smoking on risk of PD in the present study (23andMe discovery cohort and IPDGC replication cohort), and the two other Mendelian randomisation studies exploring the association between smoking and PD

	Smokers	Non-smokers	PD cases	PD proxy cases	Controls	Odds ratio (with 95% confidence interval) for never vs. ever smokers
Grover et al.	246,715	271,918	9,581	..	33,245	0.71 (0.57–0.90)
Nalls et al.	208,988	244,705	37,688	18,618	1,417,791	0.94 (0.88–1.00)
23andMe discovery cohort	1,067,699	1,457,457	19,924	..	2,413,087	0.96 (0.92–0.99)
IPDGC replication cohort	..	..	15,056	18,618	449,056	0.87 (0.76–0.99)

PD, Parkinson’s disease; IPDGC, International Parkinson’s disease Genomics Consortium.