Table 2. Associations between smoking- and quitting and PD status.

The odds ratio compares the odds of exposure (e.g. ever smoking) among PD patients, which is the numerator, and the odds of exposure (e.g. ever smoking) among population controls, which is the denominator.

	PD patients/Controls	OR^a (95% CI)	p-value
Smoking history
Non-smoker	321/325	1
Former smoker	265/288	0.81 (0.64–1.02)	0.08
Current smoker	26/78	0.34 (0.21–0.54)	<0.001
		p for trend=	<0.001
Ever smoker	291/366	0.71 (0.57–0.89)	0.003
For ever cigarette smokers only
Current vs. former smoker, %	8.9/21.3	0.38 (0.23–0.62)	<0.001
Pack-years, per 10 units, mean	2.0/2.4	0.92 (0.85–0.98)	0.01
Quitting-related characteristics (for former cigarette smokers only)
Years of smoking, yr
<20	143/131	1
20–29	51/68	0.62 (0.39–0.96)	0.03
30–39	40/53	0.67 (0.41–1.09)	0.11
≥40	31/34	0.78 (0.45–1.36)	0.38
		p for trend=	0.13
Age when quit smoking, yr
<40	137/140	1
40–49	58/59	0.98 (0.63–1.52)	0.92
50–59	42/51	0.82 (0.51–1.32)	0.41
≥60	2736	0.76 (0.43–1.34)	0.34
		p for trend=	0.26
Difficulty of quitting smoking
Remarkably easy	103/100	1
Medium	76/61	1.24 (0.80–1.93)	0.34
Extremely hard	45/73	0.62 (0.39–0.99)	0.05
		p for trend=	0.09

OR: odds ratios; CI: confidence interval.

Unconditional logistic model adjusted for index age (continuous), sex, and European ancestry.