Results

Table 1 presents the original GHS data on cigarette smoking prevalence, weekly consumption per smoker, and percentage of mainly handrolled cigarette consumption among cigarette smokers.

Table 2 compares GHS and TMA estimates of manufactured cigarette consumption per adult per year for 1971–75, 1976–80, 1981–85 and 1986–90. GHS estimates were lower by a factor averaging about 0.75 for men and 0.80 for women. Such a difference is expected because TMA, but not GHS, adjust data (upwards) to match known sales data and so correct for understatement of smoking. Also, excluding mainly handrolled cigarette consumption in the GHS estimation omits those who smoke mainly but not exclusively handrolled cigarettes included in the TMA data. As no age or time related patterns were seen in the GHS/TMA factors, 1991–95 data to include in CCTCC estimates were obtained by dividing GHS estimates by the factors of 0.75 or 0.80, as is also shown in table 2.

Table 3 gives updated CCTCC estimates for 1991–95 and also, for comparison, for 1981–85 and 1986–90. In men the estimates are declining at all ages, with the percentage reduction between 1981–85 and 1991–95 steeper at younger ages. In women, though relatively marked declines are seen at young ages, lesser declines are seen in middle age with increases seen at older ages.

An updated graphical display of the full CCTCC data will appear in LAIA factsheets and is not reproduced here.

Discussion

CCTCC was developed by Todd7 to be a simple index of lifetime tobacco exposure with some predictive value for risk of lung cancer and other chronic smoking associated diseases. Anyone using CCTCC should understand its possible limitations which include the following:

(1) CCTCC ignores the smoking of pipes, cigars or handrolled cigarettes.

(2) CCTCC assumes that exposure early and late in life are equally important in determining risk.

(3) CCTCC may not reflect changes which occur in the relative distribution of heavy and light smokers if the underlying risk-response is non-linear.

(4) Early data had to be estimated by backward extrapolation (although as surveys go back 50 years this is less of a problem now than formerly).

(5) Data had to be estimated from two surveys—the TMA until 1990 and the GHS subsequently—although the relatively consistent ratios in table 2 and the relatively small contribution of 1991–95 data to total CCTCC estimates suggest this is of minor importance.

(6) Changes in tar levels are assumed to be independent of age and sex, however available data2 suggest this may not be a major difficulty.

(7) There is some uncertainty over tar levels prior to 1965. We used TMA data suggesting that SWAT was constant at 31.4 mg/cig before 1965. Wald et al,8 based on chemical analyses conducted around 1980 of old cigarettes sent in by the public, claimed that SWAT declined before 1965. In fact, the pre-1965 SWAT levels they cited (32.9, 32.2, 29.4 and 30.4 mg/cig for 1934–40, 1941–47, 1948–54, and 1955–61, respectively) were close to the TMA figure of 31.4 mg/cig, and their lower figure of 25.5 mg/cig for 1962–68 was based on an unrepresentative sample of brands sold, predominantly towards the end of the period, when the TMA data also showed a marked decline (23.9 mg/cig in 1968). The use of Wald’s SWAT data would have little effect on CCTCC levels or trends in any case.

The most important problem with CCTCC may lie in using tar yield data, based on machine smoking under standard conditions, to index exposure to tar. Although it is reasonably clear that lower tar yields are associated with reduced mortality from lung cancer,9 and that smokers switching to lower tar brands do reduce average tar intake,10 ,11 smokers do appear to “compensate” for reduced tar (and nicotine) delivery by modifying how they smoke.12 It has been estimated that the reduction in tar intake is only about half the reduction predicted based on the published tar yields.10 ,11

In additional analyses to study effects of adjustment for compensation (data not shown), we recalculated CCTCC assuming either (1) that tar levels had not reduced since 1965 (“complete compensation”) or (2) that tar levels had reduced by the square root of the observed decline in machine yields (“partial compensation”). The decline in CCTCC in men at all ages over the period 1981–85 to 1991–95 was confirmed under both assumptions. However, the decline in CCTCC in women was only really evident below the age of 40 in the complete compensation analysis and below the age of 45 in the partial compensation analysis, compared with below the age of 65 in the analyses in table 3 which ignore compensation.