Here are some excerpts of a Surgeon General's report. The pages were scanned and Optical Character Recognition was used to extract the text. I put the tables in HTML form. Any errors were probably introduced by me.
Public Health Service. Department of Health, Education, and Welfare. Smoking and health: report of the Advisory Committee to the Surgeon General of the Public Health Service. Washington, DC: US Department of Health, Education, and Welfare, Public Health Service, 1964; DHHS publication no.(PHS)64-1103.
... For fixed amount of smoking, the mortality ratios (with one exception) exhibit consistent and rather striking increase as the age at which smoking was started decreases. This increase appear in all smoking groups of Table 8. For men who started smoking cigarettes under the age of 20, the over-all death rate was about twice that for non-smokers, whereas for theme who did not start until they were over 25 the death rate was only about 35 percent higher.

MORTALITY RATIO BY DURATION OF SMOKING

Three studies have some data available on the number of years during which the subjects had smoked. The comparison of mortality ratios for different lengths of time smoked is of interest in relation to two questions raised by Dorn (6) in an earlier analysis of the U.S. veterans' data. Is there a minimum period of use during which no effect on the death rate is noticeable? Is there a maximum period after which no increase in the relative death rate is perceptible? For current cigarette smokers the results (Table 9) are not clear-cut. In the U.S. veterans study, men smoking for less than 15 years had death rates about the same as non-smokers. There is a rise of about 50 percent in the mortality ratio for those who had smoked 15-35 years, with a further rise for those smoking longer than 35 years. The study of men in nine states shows a rise from under 25 years to 25-34 years duration, but no further rise thereafter. In the Canadian study the mortality ratio with cigarette smokers is just as high for durations less than 15 years as for durations of 15-29 years, though there is a rise (to 1.73) for smokers of cigarettes only who have been smoking more than 30 years.

Table 9 -- Mortality ratios for current smokers by type of smoking and by length of time smoked
Number of years smoked
Type of smoking U.S. veterans Canadian veterans Men in 9 States
< 15 15-24 25-34 35+ < 15 15-29 30+ < 25 25-34 35+
Cigarettes only 0.92 1.52 1.50 1.86 1.52 1.41 1.73 1.46 1.74 1.78
Cigarettes and other 1.07 1.41 1.33 1.49 1.24 1.27 1.22
Cigars only 0.92 0.94 0.96 1.12 1.06 0.81 1.31
Pipes only 1.01 1.34 0.97 1.07 1.26 0.93 1.09
Thus, all three studies show some increase in the mortality ratios with longer duration of smoking, but the pattern is irregular. In a further breakdown of the data by amount smoked, Hammond and Horn (10) found no trend with duration for men smoking more than a pack a day, but the other two studies show an upward trend for this group of smokers For cigar smokers the only groups showing an increase in death rates over non-smokers are those smoking for the longest period (Table 9). The increases of 12 percent for the 35 years or over group in the U.S. study and of 31 percent for the 30 years or over group in the Canadian study are both statistically significant.

For pipe smokers no trend with duration of smoking is discernible. The two figures which stand out (1.34 in the U.S. study and 1.36 in the Canadian study) are both based on relatively small numbers of death.

INHALATION OF SMOKE

In two of the studies the subjects were questioned as to whether they inhaled. In the study of men in 25 states each subject was asked to place himself in one of the four classes: do not inhale, inhale slightly, inhale moderately, inhale deeply. In the Canadian veterans study the subject simply classified himself as an inhaler or non-inhaler.

For current smokers of cigarettes only in the U.S. study, 6 percent of the subjects stated that they did not inhale, 14 percent inhaled slightly, 56 percent moderately and 24 percent deeply. In the Canadian study 11 percent classified themselves as non-inhalers.

Since inhalation practices may vary with the amount smoked, the results for cigarette smokers (Table 10) are given separately for different amounts. For the men in 25 states an increase in the degree of inhaling for a fixed amount of smoking is in general accompanied by an increase in the mortality ratio. The relation of inhalation to mortality appears quite marked: for instance, non-inhalers who smoke 20-39 cigarettes daily have mortality ratios no higher than moderate or deep inhalers who smoke 1-9 cigarettes daily. With the very heavy smokers (40+ ) the Figures in Table 10 suggest that the mortality ratio may remain the same for non-, slight, and moderate inhalers The ratios of 2.05 (non-) and 1.97 (slight) are, however, based on only 26 and 41 deaths, respectively.

Table 10.-- Mortality ratios for smokers of cigarettes only by inhalation status and amount of smoking
Degree of Inhalation Cigarettes per day Over-all ratio
1-9 10-19 20-39 40+
Men in 26 States:
None 1.29 1.46 1.56 2.05 1.49
Slight 1.29 1.48 1.84 1.97 1.58
Moderate 1.61 1.83 1.84 2.01 1.83
Deep 1.56 1.76 2.18 2.30 2.20
Canadian veterans(1)
None 1.05 1.11 (2) 1.03 (3) 1.08
Some 1.35 1.50 (2) 1.71 (3) 1.53
(1) Amounts are lifetime maximum amounts smoked.
(2) 10-20 cigarettes per day
(3) Over 30 cigarettes per day

Looking along the rows of the U.S. veterans study it will be seem that for each degree of inhalation the mortality ratio increased with the amount smoked. Ipsen and Pfaelser (14) have shown that the logarithms of the 16 death rates at age 61 (approximately the average age) can be adequately...

Ex-Cigar and Pipe Smokers

Mortality ratios for smokers of cigars only and pipes only who had stopped smoking prior to the date of entry are given in Table 14, the corresponding ratios for current smokers being included for comparison.

For ex-cigar smokers the mortality ratios are higher than those for non-smokers and higher than those for current smokers in all four studies presented. The same is true for ex-pipe smokers with the exception of the Canadian study.

The interpretation of this result is not clear to us. According to Hammond and Horn (10) and Dorn (6), the explanation may be that a substantial number of cigar and pipe smokers give up because they become ill: some date from cigarette smokers that support this explanation have recently been analyzed by Hammon (12). Further analysis of the U.S. veterans data indicates that mortality ratios run highest in ex-smokers who smoked heavily and for a long time.

Table 14.-- Mortality ratios for ex-smokers of cigars only and pipes only and for current cigar and pipe smokers
Type of smoker British Doctors Men in 9 States U.S. veterans Canadian veterans Men in 25 States
Ex-cigar 1.55 1.30 1.17 1.24
Current cigar 1.10 1.07 1.11 0.97
Ex-pipe 1.12 (1) 1.29 1.36 1.01 1.23
Current pipe 0.95 (1) 1.06 1.06 1.10 0.86
(1) Pipe and cigar combined.

EVALUATION OF SOURCES OF DATA

The Study Populations

Various reasons dictated the particular choices made of the seven study populations, considerations of feasibility playing an important role. None of the populations was designed, in particular, to be representative of the U.S. male population. Any answer to the question "to what general populations of men can the results be applied?", must involve an element of unverifiable judgment. However, three of the studies have populations with widespread geographic distribution within the United States, as do the British and Canadian studies within their respective countries. Taken as a whole, the seven populations offer a substantial breadth of sampling of the type of men and environmental exposures to be found in North America and Britain, as well as providing some variation in methodological approach, although the basic plan was similar in all studies.

The seven studies differ considerably in size. They vary also in the extent to which they are free from methodological weakness. The studies of men in nine states and men in 25 States, for instance, suffer from the difficulties that the populations studied are hard to define, that the smokers and non-smokers were recruited by a large number of volunteer workers, and that completeness in the reporting of deaths was bard to achieve, since this depends on report from the volunteers. On the other hand these studies have the advantage of being large and of having a broad geographic representation of the U.S. male population, while the second study is the only one that attempts to investigate many other relevant variables in which smokers and non-smokers may differ. In the California occupational study the focus of interest is occupational differences in lung cancer mortality, smoking history being recorded primarily in order to be able to adjust comparisons among different occupational groups for differences in amount smoked. In the analysis we have not attempted to rate the studies as to over-all quality or to assign differential weights to their results, except that in the smaller studies it is recognized that mortality ratios ere subject to larger sampling errors. Our attitude is to attach importance only to results that appear to be generally confirmed by the studies.

Some idea of the relative death rates in these studies as compared with the 1960 white male population of the United States is given in Table 15, which shows the age-adjusted death rates for ages 35 and over, using the age distribution of the U.S. white male population as a standard. (The choice of 1960 for the comparison is arbitrary, but the white male rate changed little between 1955 and 1960.)

In all studies the death rates for non-smokers are markedly below those of U.S. white males in 1960. Even the smokers of one pack of cigarettes or more daily have death rates that average slightly below the U.S. white male figure. To some extent this is to be expected, since hospitalized and other seriously ill persons are not recruited in such studies. The sizes of the differences appear, however, surprising for the studies with United States population. Hammond and Horn (10), in a special investigation on this question, concluded that the discrepancy in their study was due to the screening out of sick persons in recruiting plus probably a selection toward men of higher economic levels. They point out that their death rates are substantially above those for males who had held ordinary life insurance policies for from...

Table 15.-- Age-adjusted death rates per 1,000 man-years for current smokers of cigarettes only (aged 35 and over), by amount smoked, in seven studies and for U.S. white males
Study Non-smokers Current smokers of cigarettes only U.S. white males, 1960
Less than 1 pack 1 pack or more
British Doctors 15.8 19.2 23.3 22.9
Men in 9 States 14.4 (1) 22.4 (1) 27.1 (1) 22.6 (1)
U.S. Veterans 12.0 18.1 23.9 22.9
California occupational 10.5 (1) 14.2 (1) 18.0 (1) 22.5 (1)
California legion 11.3 16.4 16.3 22.9
Canadian veterans 14.1 22.1 24.2 22.9
Men in 25 States 12.8 (2) 18.1 (2) 19.2 (2) 22.9
(1) Ages 50-69
(2) These figures may be too low be about 1.7 percent, since the person-years used in the computation included some contribution by men who had not been fully traced.