Statistics in a Rate Matrix

A Rate session can be used to calculate crude rates, age-adjusted rates, or trends based on either type of rate. The results matrix will always include either a crude or age-adjusted rate:

• Rate (crude) - 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.

• Rate (age-adjusted) - 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.

If the matrix does not include trend statistics, then it may contain the following statistics. Counts and populations are always included; the standard errors and confidence intervals must be selected on the Statistic tab.

• Count - number of cases associated with the rate

• Pop - the population counts are the sum of the populations for all years included in the calculation of the associated rate

• Standard Population

• Standard Error

• Lower Confidence Interval (CI)

• Upper Confidence Interval (CI)

If the results matrix shows trends in rates, then it may include the following statistics. The P-values are only shown if checked on the Statistic tab.

• Percent Change (PC)

• Annual Percent Change (APC)

• Standard Error

• Lower Confidence Interval (CI)

• Upper Confidence Interval (CI)

• P-values for APC Significance Testing (SE/P)

If you chose to include rate ratios on last row variable groupings, then the results matrix will include the following columns. These cells will always be blank for the first grouping of the innermost row variable (since it is the reference grouping). Subsequent rows contain data comparing that row's grouping to the first grouping.

• Rate Ratio - this grouping's rate divided by the reference (first) grouping's rate.

• Ratio Lower Confidence Interval (CI) - the lower bound of the confidence interval for the rate ratio in this row. If this is greater than 1, the ratio will be flagged as significant. When the rate ratio is significantly different from 1, the two rates being compared are considered significantly different from one another.

• Ratio Upper Confidence Interval (CI) - the upper bound of the confidence interval for the rate ratio in this row. If this is less than 1, the ratio will be flagged as significant. When the rate ratio is significantly different from 1, the two rates being compared are considered significantly different from one another.

• Ratio P-Value - the largest p-value at which the ratio would be flagged as significant.