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# Glossary of Statistical Terms

• Updated: 12/08/2009

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The Glossary of Statistical Terms includes brief definitions and plain language explanations for common statistical terms. Five key statistical measures of cancer - incidence, mortality, survival, prevalence, and lifetime risk - are more fully explained with "Read more" links, below. NCI monitors these cancer statistics to assess progress and to identify population subgroups and geographic areas in which cancer control efforts need to be concentrated.

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age-adjusted rate
An age-adjusted incidence or mortality rate is a weighted average of the age-specific incidence or mortality rates, where the weights are the proportions of persons in the corresponding age groups of a standard million population. The potential confounding effect of age is reduced when comparing age-adjusted rates computed using the same standard million population.

annual percent change (APC)
Annual Percent Change is used to measure trend or the change in rate over time. It is the "average" annual rate of change over the time series selected.

Annual Report to the Nation
An annual update of cancer death rates, incidence rates (new cases), and trends in the United States. The Centers for Disease Control and Prevention, the American Cancer Society, the National Cancer Institute, and the North American Association of Central Cancer Registries collaborate to create this report.

cancer burden
A measure of the incidence of cancer within the population and an estimate of the financial, emotional, or social impact it creates. The burden of disease is not borne equally by all population groups in the United States.

Cancer Statistics Review (CSR)
An annual report containing the most recent incidence, mortality, and survival statistics, published by the Cancer Statistics Branch of the NCI. It presents a broad profile of the cancer burden.

complete prevalence
Complete Prevalence represents the proportion of people alive on a certain day who previously had a diagnosis of the disease, regardless of how long ago the diagnosis was, or if the patient is still under treatment or is considered cured.

confidence interval
A range of values that has a specified probability of containing the rate or trend. The 95% (p-value = .05) and 99% (p-value = .01) confidence intervals are the most commonly used.

crude rate
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.

delay adjusted rate
A cancer rate adjusted for reporting delay, the time elapsed before a diagnosed cancer case is reported to the NCI.

extent of disease
Refers to the stage of the disease and details the degree to which the cancer has advanced. Extent of disease records the number of lymph nodes involved, metastases and size of primary tumor

Fast Stats
Fast Stats is designed to allow quick and easy access to key statistics for all major cancer sites by age, sex, race, and geographic area. The statistics include incidence, mortality, prevalence, and the probability of developing or dying from cancer.

five-year survival rate
The percentage of people in a study or treatment group who are alive five years after they were diagnosed with or treated for a disease, such as cancer. The disease may or may not have come back.

georeferenced statistics
Statistics reported by geographic location of the events (e.g., residence of the cancer case)

ICCC classification
At the time the World Health Organization's (WHO) International Agency for Research on Cancer (IARC) published their first monograph on Childhood Cancer in 1988, Dr. R. Marsden published an annex giving a classification scheme for childhood cancer that consisted of 12 groups based chiefly on histologic type. The classification by Marsden has been modified and is now called the International Classification of Childhood Cancers.

incidence
The number of newly diagnosed cases during a specific time period. Read more >

Joinpoint software
Statistical software for the analysis of trends using a regression model that describes trends by a sequence of straight line segments, connected at "joinpoints" where significant changes in trend have been calculated.

life tables
A table for a given population listing, for each sex and each age from 0 to 120, how many members die at that age and how many survive one more year.

lifetime risk
The probability of developing or dying from cancer in the course of one's lifespan. Read more >

limited-duration prevalence
Represents the proportion of people alive on a certain day who had a diagnosis of the disease within the past x years.

mortality
The number of deaths during a specific time period. Read more >

percent change
The percent change (PC) in a statistic over a given time interval is Percent change = (Final value - Initial value) / Initial value * 100. A positive PC corresponds to an increasing trend, a negative PC to a decreasing trend.

prevalence
The number of cases alive on a certain date. Read more >

primary tumor
The original tumor.

progression-free survival
The length of time during and after treatment in which a patient is living with a disease that does not get worse. Progression-free survival may be used in a clinical study or trial to help find out how well a new treatment works.

relative survival rate
A specific measurement of survival where the rate is calculated by adjusting the rate to remove all causes of death except cancer. It is the ratio of a cancer patient's chance of surviving a given time interval to that of an average person of the same age and sex.

reporting delay
The time elapsed before a diagnosed cancer case is reported to the NCI. Currently, the NCI allows a standard delay of 22 months between the end of the diagnosis year and the time the cancers are first reported to the NCI in November, almost two years later.

SEER
Surveillance, Epidemiology, and End Results (SEER) Program of the NCI is a collection of population-based cancer registries in the United States which collect and submit cancer incidence and follow up data to the National Cancer Institute. The National Cancer Act of 1971 mandated the collection, analysis, and dissemination of data useful in the prevention, diagnosis, and treatment of cancer leading to the establishment of the SEER Program.

SEER registries
SEER Program collects cancer incidence and survival data from the SEER registries, geographic areas selected for inclusion in the SEER Program based on their ability to operate and maintain a high quality population-based cancer reporting system and for their epidemiologically significant population subgroups.

spatial correlation
A measure of the tendency for places that are near to each other to have more similar (positive correlation) or dissimilar (negative correlation) values of their statistics.

stage
The extent of a cancer within the body. If the cancer has spread, the stage describes how far it has spread from the original site to other parts of the body.

standard error
The standard error of a rate is a measure of the sampling variability of the rate.

standard million population
A standard million population for a geographic area is a table giving the number of persons in each age group 0, 1-4, ... , 85+ out of a theoretical cohort of 1,000,000 persons that is distributed by age in the same proportions as the population.

standard population
A standard population for a geographic area, such as the U.S. or the world, is a table giving the proportions of the population falling into the age groups 0, 1-4, 5-9,…, 80-84, and 85+.

statistically significant
Describes a mathematical measure of difference between groups. The difference is said to be statistically significant if it is greater than what might be expected to happen by chance alone.

surveillance data (cancer)
Measures of cancer incidence, morbidity, survival, and mortality for persons with cancer. It also includes the assessment of genetic predisposition, environmental and behavioral risk factors, screening practices, and the quality of care from prevention through palliation.

survival
The proportion of patients alive at some point after the diagnosis of their cancer. Read more >

trends over time
The change in rate over time expressed as an annual percent change.

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