RE: AW: Tooth fairy inspired law suit

["Doty, Patrick" <fpdoty@SANDIA.GOV>]

The CDC appears to endorse the idea that statistically significant clusters

exist.  The text below was copied from the website

http://www.cdc.gov/nceh/clusters/about_clusters.htm



Definition



A cancer cluster is defined as a greater-than-expected number of cancer

cases that occurs within a group of people in a geographic area over a

period of time.



Challenges in identifying 



The complex nature of cancer makes it inherently challenging to identify,

interpret, and address cancer clusters.  



"Cancer" is a term representing many diseases with a variety of causes. The

time between exposure to a cancer-causing agent, or the existence of other

risk factors, and the development of cancer can be decades; therefore,

causes are hard, and in some cases impossible, to identify.  



Cancer in general is common. Since 1990, about 16 million new cancer cases

have been diagnosed, according to the American Cancer Society (Cancer Facts

and Figures 2002). About 1,284,900 new cancer cases are expected to be

diagnosed in 2002.



Cancer rates vary by age, race, gender, risk-factors, and type. We know that

risk for cancer increases with age and that cancer is caused by both

external factors (e.g., tobacco, chemicals, radiation, and infectious

organisms) and internal factors (e.g., inherited mutations, hormones, immune

conditions). Nutrition, physical inactivity, obesity, and other lifestyle

factors also play a role in cancer risk and outcomes. These factors may act

together or in sequence to initiate or promote cancer. Ten or more years

often pass between exposures or mutations and detectable cancer.



Some racial and ethnic groups have a higher incidence of and deaths due to

cancer. Such disparities may be due to multiple factors, such as late stage

of disease at diagnosis, barriers to health care access, history of other

diseases, biologic and genetic differences, health behaviors, differences in

exposures to carcinogens in the environment and the workplace, and other

risk factors.



Characteristics



What first appears to be a cancer cluster may not be one after all. A review

of the situation may show that the number of new cancer cases is in the

expected range for the population and therefore that the cases do not

represent a cancer cluster. Cancer cases are more likely to represent a

cancer cluster if they involve (1) one type of cancer, (2) a rare type of

cancer, or (3) a type of cancer in a group not usually affected by that

cancer, such as a cancer in children that is normally seen in adults.

However, cases of common cancers are those most often perceived and reported

by the public as being part of a cancer cluster. 



Identification



The investigators develop a "case" definition, a time period of concern, and

the population at risk. They then calculate the expected number of cases and

compare them to the observed number. A cluster is confirmed when the

observed/expected ratio is greater than 1.0, and the difference is

statistically significant. 



Usually, a local or state health department provides the first response to a

suspected cancer cluster. The local or state health department gathers

information about the suspected cancer cluster (e.g., types of cancer,

number of cases, addresses and occupations of those people with cancer,

possible causes), develops and applies the case definition, and determines

whether there is a greater-than-expected number of cases.   



Interpretation



Confirmation of a cancer cluster does not necessarily mean that there is any

single, external cause or hazard that can be addressed. A confirmed cancer

cluster could be the result of any of the following: 



chance 

miscalculation of the expected number of cancer cases (e.g., not considering

a risk factor within the population at risk) 

differences in the case definition between observed cases and expected cases



known causes of cancer (e.g., smoking) 

unknown cause(s) of cancer. 

Follow-up investigations can be done, but can take years to complete and the

results are generally inconclusive (e.g., usually, no cause is found). 



Reporting



If you suspect a cancer cluster in your community or  workplace, or if you'd

like information such as cancer statistics or trends in your area, first

contact your local or state health department or state cancer registry. For

information about how to contact your state or local health department, go

to http://www.cdc.gov/other.htm#states. For state cancer registry contact

information, go to http://www.cdc.gov/cancer/npcr/statecon.htm#list.  



Prevention and Early Detection



Concern about cancer and cancer clusters provides an opportunity for people

to learn about how they can prevent cancer or identify it early. Sixty-five

percent of public inquiries about cancer clusters involve cancers for which

screening and preventive measures exist. The best steps that people can take

regarding cancer are to (1) educate themselves about their personal risk and

risk factors for cancer, (2) avoid these risks, and (3) take advantage of

recommended cancer screenings. 



The following Web sites provide information on cancer 



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