GRAPHICAL PRESENTATION OF TRENDS IN RATES

A variety of graphical approaches have been used to visually portray a nd analyze temporal trends, especially annual rates of change, in dise ase rates. In reviewing their own work, the authors have found that th ey could improve on their graphical presentations by choosing an arith metic or logarithmic scale according to the research question being ad dressed, by selecting scaling ratios of the axes that allow one to det ect specific rates of change, and by using uniform scaling ratios to f acilitate comparisons across graphs. Different presentations of the sa me data can result in different impressions. The authors used rates ov er a 40-year period to illustrate the concepts involved and to investi gate the portrayal of various rates of change. These principles extend to the plotting of odds ratios or relative risks, where the choice of an arithmetic rather than a logarithmic axis also can result in a mis leading plot. The authors conclude that a graph should be designed and studied with care, clearly reflect the truth, convey information, and make a point without overemphasizing. For the particular problem addr essed here, displaying temporal trends in disease rates, they see adva ntages in justifiable uniformity. Attention to plotting techniques in the epidemiologic and medical literature should be encouraged.