Trends and predictions for gastric cancer mortality in Brazil

Time trends for population-based disease rates often are summarized by using direct adjustment by period of diagnosis or death. Similarly, the effect of age often is presented graphically as age-specific rates for a given period of diagnosis. These approaches may be necessary if there is an absence of long-term data, as they provide a natural way for annually updating information when monitoring trends, or they may be a convenient way of summarizing a large amount of data (7, 10, 11, 39, 45). However, these summaries only can adjust for the effect of age in a given period; they implicitly ignore the cohort effect. The effect of cohort is an important factor in understanding time trends for many diseases. Thus, it is not advisable to use data analytic strategies that routinely ignore it. Another alternative to modeling is to give a graphical presentation of the age-specific rates themselves. As I noted in the introduction, some of the first analyses to identify the effect of cohort on diseases, such as tuberculosis and lung cancer, relied entirely on a graphical analysis. Although graphs certainly are an important part of the interpretation of time trends, it would be a mistake to limit your analysis to impressions of points on a graph. For example, such a perusal would not give an objective indication of the statistical significance of a particular pattern. Regression analysis forces us to recognize a fundamental problem with interpreting time trends in disease rates--a problem that you should remember, even when trying to understand a graphical display of time trends in age-specific rates.

Use of tobacco, moderate to heavy alcohol ingestion, infrequent consumption of raw fruits and vegetables, and low income accounted for more [figure: see text] than 98% of the SCE rates among both African American and white men and for 99% of the excess incidence among African Americans compared to whites in a case-control study in three areas of the United States [14]. Thus, it is likely that declines in the prevalence of smoking and drinking, especially among men, and increased intake of fresh fruits and vegetables may have contributed to the downward incidence and mortality rate trends reported for SCE. In addition, it seems plausible that obesity, GERD, and possibly reductions in H. pylori prevalence have contributed to the upward trends in ACE rates. Reductions in smoking, improved diet, and reductions in H. pylori prevalence probably have contributed to the consistent reductions observed for NGA. Contributing factors are less clear for the rising incidence rates of GCA during the 1970s and 1980s. These incidence rates have not continued to rise in recent years.