# Statistic for Rate Sessions

In the Statistic section of the Statistic tab, you must first choose whether to calculate crude rates, age-adjusted rates, or trends in rates over time. The statistic you choose will determine the parameters you need to set.

#### Crude Rates

A crude rate is the number of new cases (or deaths) occurring in a specified population per year, usually expressed as the number of cases per 100,000 population at risk. SEER*Stat allows you to display rates as cases per 1,000; 10,000; 100,000; or 1,000,000. When you calculate crude rates, the results matrix will include the counts and populations used to calculate the rates. Note that the population counts are the sum of the populations for all years included in the rate.

#### Age-adjusted Rates

An age-adjusted rate is a weighted average of the crude rates, where the weights are the proportions of persons in the corresponding age groups of a standard population. The potential confounding effect of age is reduced when comparing age-adjusted rates computed using the same standard population. When calculating age-adjusted rates, the results matrix will include the associated counts and population counts. Note that the population counts are the sum of the populations for all years included in the rate.

#### Trends (Crude or Age-adjusted)

Trends in crude or age-adjusted rates are expressed in two forms: the percent change (PC) and the annual percent change (APC). Note that age adjustment minimizes the effect of a difference in age distributions when analyzing trends.

• PC = ((end rate - initial rate) / initial rate) * 100.  Either a one-year rate or the unweighted average of two one-year rates can be used for the initial and end rates.

• The APC is calculated by fitting a regression line to the natural logarithm of the rates (r) using the calendar year (x) as a regressor variable, i.e., y = mx + b where y = ln(r). You may also utilize the standard errors of the rates to fit to a weighted least squares regression line.