Cigarette smoking is the leading cause of preventable death in the United States and kills more Americans than AIDS, alcohol, illegal drug use, car accidents, fires, murders and suicides combined. It has been estimated that 430,000 Americans die from smoking every year. Fighting tobacco use is, consequently, one of the major public health goals of our time and there are now many programs available designed to help smokers quit. One of the major aids used in these programs is nicotine chewing gum, which acts as a substitute oral activity and provides a source of nicotine that reduces the withdrawal symptoms experienced when smoking is stopped. But separate randomised clinical trials of nicotine gum have been largely inconclusive, leading Silagy (2003) to consider combining the results from 26 such studies found from an extensive literature search. The results of these trials in terms of numbers of people in the treatment arm and the control arm who stopped smoking for at least 6 months after treatment are given in Table 15.1. Bacille Calmette Guerin (BCG) is the most widely used vaccination in the
world. Developed in the 1930s and made of a live, weakened strain of Mycobacterium bovis, the BCG is the only vaccination available against tuberculosis (TBC) today. Colditz et al. (1994) report data from 13 clinical trials of BCG vaccine each investigating its efficacy in the prevention of tuberculosis. The number of subjects suffering from TB with or without BCG vaccination are given in Table 15.2. In addition, the table contains the values of two other variables for each study, namely, the geographic latitude of the place where the study was undertaken and the year of publication. These two variables will be used to investigate and perhaps explain any heterogeneity among the studies.