CP*Trends: An Online Tool to Compare Cohort and Period Trends Across Cancer Sites.

Cohort or period components of trend can provide a rationale for new research or point to clues of effectiveness for control strategies. Graphical display of trends guides models that quantify the experience of a population. A method for smoothing rates by single years of age and year are developed and displayed to show the contribution of period and cohort on trend. The magnitude of the contribution of period and/or cohort in a model for trends may be assessed by percent deviance explained and relative contribution of cohort and period individually, C-P Score. The method is illustrated using lung and bronchus cancer mortality in females, and prostate and colorectal cancer incidence in males. Smoothed age-period and age-cohort rates provide a useful first step in studies of etiology and impact of disease control without imposing a restrictive model. Cohort predominates for female lung and bronchus cancer and period for male prostate cancer. However, the effects change with age for male colorectal cancer incidence, indicating an age shift in relevant exposures. These methods are applied in an interactive website for both incidence and mortality in over 20 cancer sites in the US.