is the natural logarithm of the RR; for small values of β (e.g., −.09 to 0.09), the RR can be approximated by 1+β with accuracy to the second decimal place and the average annual percentage change is 100*β. We sometimes refer to the estimated 10-year percentage change for a given outcome and/or group, which can be calculated as 100*(RR10-1). To account for changes in item content, such as the switch to a four-drink binge-drinking threshold for women, we incorporate dummy variables into the model to estimate separate intercepts for years assessed with separately worded items, while assuming a constant slope. Accordingly, the change from a five- to a four-drink threshold will appear as a step-function in the modeled trend line (see Figure 1). An additional dummy variable was incorporated to account for a major redesign in the BRFSS in 2011 (Centers for Disease Control and Prevention, 2012).
