Using the Negative Exponential Model to Describe Changes in Risk of Smoking-Related Diseases following Changes in Exposure to Tobacco

Table 1

Summary of lung cancer results for reducing amount smoked from three prospective studies.

Characteristic	Study 1 [148]	Study 2 [149]	Study 3 [150]
Location	Denmark	Norway	Korea
Sex	M and F combined	M, F	M
Time between the two examinations (years)	5 to 10	3 to 13	2
Follow-up period from examination two (years)	18	21.2	10.7
Definition of a continuing smoker ( subjects)	Heavy smoker (at least 15 cigs/day) at each exam ( 7351)	Heavy smoker (at least 15 cigs/day) at each exam ( 4739M, 1831F)	At each exam subjects were described as heavy (20+, 57730), moderate (10–19, 101347), or light (<10 cigs/day, 76754)
Definition of a reducing smoker ( subjects)	() Heavy smoker at first exam reducing by at least 50% at the second exam ( 832)	() As for study 1, males ( 348)	() Heavy smoker at first exam reducing to moderate smoker at second exam ( 15936)
		() As for study 1, females ( 127)	() Heavy to light ( 4293)
			() Moderate to light ( 19168)
Ratio of average consumption at the two exams in reducers ()	() 8.5/20.2 = 0.42	() 9.7/22.9 = 0.42	() 0.50
		() 8.6/19.5 = 0.44	() 0.17
			() 0.33
Time from reduction to end of follow-up (years)^a	21.4	24.0	11.7
Cases in reducers	() 52	() 10	() 63
		() 2	() 95
			() 53
Average age at the time of reduction (years) ()	() 49.0	() 39.0	() 42.6
		() 38.2	() 42.9
			() 42.4
Observed RRs (95% CIs)^b	() 0.73 (0.54–0.98)	() 0.71 (0.36–1.39)	() 0.72 (0.59–0.89)
		() 0.51 (0.12–2.08)	() 0.63 (0.46–0.86)
			() 0.79 (0.64–0.98)
NEM predicted RRs	() 0.64	() 0.60	() 0.80
		() 0.61	() 0.67
			() 0.73

Estimated as the time of follow-up plus half the time between the two examinations.
Reducers relative to continuing smokers.