Direct Incidence Rates for Cancer
Cancer incidence is the number of new cancer diagnoses in a defined population over a specific time period. A direct incidence rate is the most appropriate statistic to compare cancer incidence in one relatively large area to another relatively large area (such as one county to another or one state to another). For example, direct age-adjusted incidence rates might be used to determine whether prostate cancer occurred more frequently in Suffolk County vs. Norfolk County. The MA EPHT website reports direct rates for Massachusetts at the county and statewide levels.
All direct rates are age-adjusted because cancers do not impact different age groups equally.
One calculation will generate:
- The number of diagnoses
- An age-adjusted cancer incidence rate
Example: Age adjustment
Prostate cancer is more common among older men. A county containing 10,000 men over the age of 50 would naturally have more prostate cancer diagnoses than a county containing only 2,000 men over 50. In order to accurately compare prostate cancer in these two counties, we must adjust for their different age structures.
Example: Comparing direct rates between two counties
Let's say a county had a direct age-adjusted rate of 9.4 for prostate cancer and another county had a rate of 8.0. This would mean that prostate cancer occurred at a rate of 9.4 cancer diagnoses per 100,000 people over a 5-year time period in the first county, and at a rate of 8.0 cancer diagnoses per 100,000 people over the same 5-year period for the second county. Since we have accounted for the different age structures of the counties, we can compare the two rates and conclude that the first county had a higher rate of prostate cancer during this time period than the second county.
|Cancer Type||County||Count||Cancer rate (per 100,000)|
|Cancer Type Prostate||County County 1||Count 12||Cancer rate (per 100,000) 9.4|
|Cancer Type Prostate||County County 2||Count 13||Cancer rate (per 100,000) 8.0|
|Data Source: Massachusetts Cancer Registry|
For more information on direct incidence rates for cancer, see the FAQ.
- Data Considerations
When reviewing and interpreting cancer data, it is important to consider the following:
- Direct rates have been adjusted for different age distributions and are directly comparable between two geographic areas.
- Counts and rates are calculated based upon residential address at the time of diagnosis. No information is available on prior residences.
- Geocoding accuracy, level of geocoding, and geocoding completeness may vary by time and space. This could potentially create geographically non-random errors in calculated rates of cancer.
- No personal exposure information is available, including smoking history, diet, lifestyle, or history of cancer.
- To protect privacy, no information is shown that could identify an individual. Data suppression rules govern the release of small case counts.
- Numbers and rates may differ slightly from those contained in other publications. These differences may be due to file updates, differences in calculation methods (such as grouping ages differently or rounding off numbers at different points in calculations), and updates or differences in population estimates.
- Available Data on Cancer Direct Rates
Use the Explore Maps & Tables link to access the following measures. The most current available data will be shown. Be sure to check the site periodically for new data as it becomes available. Direct rates are presented by county or statewide for individuals of all ages for 15 types of cancer as well as two leukemia subtypes (acute myeloid leukemia and chronic lymphocytic leukemia).
- Direct rates are presented for childhood cancers for two age groups (0-15 and 0-19 years of age) for cancers of the brain and central nervous system as well as for leukemia and two subtypes of leukemia (acute lymphoid leukemia and acute myeloid leukemia).
- Annual rates are available on a statewide level. Average 5-year rates are available at the county and state levels. Due to small numbers, only 5-year average rates are presented for childhood cancers at the state level.