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Glossary of Statistical Terms

The Glossary of Statistical Terms includes brief definitions and plain language explanations for common statistical terms. The five key statistical measures of cancer - incidence, mortality, survival, prevalence, and lifetime risk - are more fully explained 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 new cancers of a specific site/type occurring in a specified population during a year, usually expressed as the number of cancers per 100,000 population at risk. That is, Incidence Rate = (New Cancers / Population) × 100,000.

The numerator of the incidence rate is the number of new cancers; the denominator is the size of the population. The number of new cancers may include multiple primary cancers occurring in one patient. The primary site reported is the site of origin and not the metastatic site. In general, the incidence rate would not include recurrences. The population used depends on the rate to be calculated. For cancer sites that occur in only one sex, the sex-specific population (e.g., females for cervical cancer) is used.

An age-adjusted rate is a weighted average of the age-specific 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.

NCI has a variety of published reports and research tools for finding incidence statistics.


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. Lifetime and age-conditional risk estimates provide a useful summary of the current cancer risk and how this risk compares with earlier periods and among select subgroups of society. These reported estimates have the potential to promote early detection efforts, to increase cancer awareness, and to serve as an aid in study planning.

Statistical models are used to compute the probability of developing or dying of cancer from birth or conditional on a certain age. The development of this statistical methodology is described on the Surveillance Research Program Web site.

NCI has a variety of published reports and research tools for finding statistics on lifetime risk.


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, with cancer as the underlying cause of death, occurring in a specified population during a year. Cancer mortality is usually expressed as the number of deaths due to cancer per 100,000 population. That is, Mortality Rate = (Cancer Deaths / Population) × 100,000.

The numerator of the mortality rate is the number of deaths; the denominator is the size of the population. The population used depends on the rate to be calculated. For cancer sites that occur in only one sex, the sex-specific population (e.g., females for cervical cancer) is used. The mortality rate can be computed for a given cancer site or for all cancers combined.

NCI has a variety of published reports and research tools for finding mortality statistics.


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 in a population who previously had a diagnosis of the disease. It includes new (incidence) and pre-existing cases, and is a function of both past incidence and survival. Information on prevalence can be used for health planning, resource allocation, and an estimate of cancer survivorship. Overview of Cancer Prevalence Statistics contains a description of the types of and methodology for calculating prevalence statistics.

NCI has a variety of published reports and research tools for finding prevalence statistics.

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 subsequent to the diagnosis of their cancer. Relative survival is an estimate of the percentage of patients who would be expected to survive the effects of their cancer. Observed survival is the actual percentage of patients still alive at some specified time after diagnosis of cancer. Survival considers deaths from all causes, cancer or otherwise. Overview of Population-based Cancer Survival Statistics contains a more detailed description and information on the interpretation of survival statistics.

NCI has a variety of published reports and research tools for finding survival statistics.


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

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  • Updated: December 8, 2009