Updated CP*Trends: an online tool to compare cohort and period trends across cancer sites

CP*Trends is a widely used Surveillance, Epidemiology, and End Results Program (SEER) website used to explore temporal effects of period and cohort on cancer incidence and mortality. It provides a graphical display of smoothed rates, and a C-P score that helps to assess the magnitude of the effect of cohort and period. This update provides results for African Americans and Whites. The C-P score has an intrinsic bias favoring cohort because there are many more cohorts than periods. An adjusted C-P score removes some of this advantage. Bootstrap confidence intervals are given, which allow one to see the effects of different sample sizes on the model results. Finally, users may control window size used in the smoothing algorithm, which helps to avoid oversmoothing or masking of trends. The method is illustrated using data on cervical cancer incidence trends for African Americans and Whites, 1975-2018. Rates are higher for African Americans, and both races have contributions for cohort. However, the period effect is only strongly evident in Whites. Visual inspection of White trends suggests possible differences for those older and younger than age 50. These methods are applied in an interactive website displaying incidence and mortality trends for over 20 cancer sites in the United States.