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Cancer Surveillance On-Line
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Glossary

95% Confidence Interval:
The range of values within which, 95% of the time, the true value would fall. The wider the range, the fewer the number of cancer cases and the more the numbers fluctuate. For example, if the 95% confidence interval is 1.0-15.0, the uncertainty is larger than if the confidence interval is 1.5-1.7.

Age:
In epidemiology, the age at which the cancer was diagnosed. The term NS-ND means not stated / non déclaré.

Age-specific Rate:
The number of cases per 100,000 persons per year for a specific, narrow age range. Five-year age groups are commonly used.

Age-standardized Rate:
A procedure where weighted averages of age-specific rates are used to modify rates to a standard population in order to minimize the effects of differences in the age composition of given populations (such as provinces or census divisions) when comparing rates for these populations. Since cancer is more common in older age groups, a population that is older will have a higher crude incidence rate. The purpose of this rate is to compare groups of people from different backgrounds and age structures, for example when comparing breast cancer between countries, a world population is used, so that the difference in incidence rates is not due to one country having older citizens. The age-standardized rates for both sexes combined also adjust for possible differences in the gender distribution.

Case Fatality Ratio:
The ratio between the number of deaths and the number of new cases of a particular cancer. This provides a crude measure of potential survival. If the case fatality ratio is 50%, then one would expect half of those diagnosed with that disease to eventually pass away.

Census Division:
A general term applying to counties, regional districts, regional municipalities, etc. In Newfoundland, Manitoba, Saskatchewan, and Alberta, the term describes geographical areas that have been created by Statistics Canada in co-operation with the provinces.

Comparative Incidence Figure (CIF):
A ratio of the age-standardized incidence rate for a disease in a specific area compared with the incidence rate for all of Canada. Those areas with a CIF less than one have an incidence rate that is less than the Canadian average. If the CIF is above one, then the area has a higher rate of disease than the rest of Canada.

Comparative Mortality Figure (CMF):
A ratio of the age-standardized mortality rate for a disease in a specific area compared with the mortality rate for all of Canada. Those areas with a CMF less than one have a mortality rate that is less than the Canadian average. If the CMF is above one, then the area has a higher rate of disease than the rest of Canada.

Confounder:
Confounding bias is caused by the presence of an extraneous factor associated with both an exposure under study and a disease outcome. A commonly used method to adjust for a potential confounder is stratification in which the comparison between exposure and disease is done at specific levels of the potential confounder. When a study mentions that they controlled for a factor, they have tried to remove the effect of that variable.

While confounding is a bias which an investigator wishes to eliminate, effect modification refers to a difference in the magnitude of an effect measure across levels of another variable. An example is throat cancer (disease) and high alcohol use (risk factor). An effect modifier is smoking, since the relative risk for alcohol has been reported to be greater at higher levels of smoking. More accurately this should be called risk-ratio modification since effect modification also depends on the risk scale for the outcome, for example risk ratio or risk difference.

Crude Rate:
The number of new cases or deaths due to a disease over the total population that could be affected, without considering age or other factors. It is usually expressed as a rate per 100,000 persons per year.

Ecumene:
A geographic term for significantly inhabited regions. Populated areas are shaded in their appropriate colour providing they have a minimum population density of about 0.4 person per square kilometres (approximately 1 person per square mile).

Epidemiology:
The study of the distribution and determinants of disease.

Geographic Variation:
See Variation. When looking at cancer incidence by Census Division, one will notice that some rates in areas are higher than in others. The inherent difficulty is in finding out if there is a reason for the higher or lower rates other than chance. Provincial registration practices can also play a role.

Hospital Separations:
The number of people who leave a hospital either through a completed procedure, discharge or death. It is often used to examine the trends in morbidity from a disease. In this context, it does not include any out-patient procedures.

ICD-9:
International Classification of Diseases, 9th edition. It is no longer the standard method of coding of disease. It was used for coding cancer incidence to 2000 and for coding mortality to 1999.

ICD-10:
International Classification of Diseases, 10th edition. It is the current standard method of coding mortality, and is used on this website.

ICDO-3:
International Classification of Diseases for Oncology, 3rd edition. It is the current standard method of coding cancer incidence, and is used on this website.

Incidence:
The number of new cases of disease during a period of time (see Prevalence).

Inference (from data):
The conclusions that one is able to draw from the data. Sometimes the numbers do not tell the whole story. Please see the section on How to use Canadian Cancer Surveillance On-Line. For instance it may seem that one area on a map has a particularly high cancer rate, when in fact it could be just be chance that the cases occurred that year. By checking the rates before and after, one would notice that the rates are more like the average over time. The statistical significance of the rate should also be considered.

Lead-time (bias):
A misleading factor that may lead one to think that screening causes increased survival when it does not. If an average person only survives 5 years with a particular cancer, but if diagnosed 5 years earlier, they may show 10 years survival when in fact they are not surviving longer with the cancer, they are just aware of it longer.

Logarithmic Scale:
A mathematical scale used for examining the rate of change. The units are based on the power of ten, i.e. 0.1, 1, 10, 100, 1,000, etc. It is useful when the rates under study vary considerably.

Morbidity:
Illness from a particular disease.

Mortality:
Death from a particular disease.

Observation:
A single new case of cancer, cancer death or hospital separation.

Prevalence:
The number of people in a particular area who currently have a disease and have not been cured of it.

Probability:
The chances or odds of something occurring. For example, the probability of a coin turning up heads is 50%.

Rate:
The proportion of a group affected over a period of time such as a year. It is usually expressed as new cases (or deaths, separations, etc.) per 100,000 people per year.

Risk:
The chance that a person may eventually develop a particular disease. When comparing two groups this can be expressed as a relative risk of disease or the odds of a disease.

Risk Factor:
A risk factor is a factor associated with an increase in the chances of getting a disease; it may be a cause or simply a risk marker. Factors associated with decreased risk are known as protective.

Screening:
The testing of an apparently healthy group of people to separate those who are likely to have a disease from those who probably don't; e.g. with a Pap smear or mammogram. Screening must be followed up with more complicated diagnostic testing to confirm that the disease is truly present.

Sensitivity:
In a screening test, is the proportion of those whose screening test was positive who, on diagnostic testing, turned out to have the disease.

Specificity:
In a screening test, is the proportion of those whose screening test was negative who were truly free of disease.

Standard Population:
A population distribution that is used to create rates that have the same age structure, so that different rates can be properly compared. See age-standardized rates.

Standard Deviation:
A measure of how much variation there is in the values around the average number or rate.

Standardized Incidence Ratio (SIR):
The ratio of the observed to the expected new cases of cancer; the expected number is based on the age-specific rates for all of Canada.

Standardized Mortality Ratio (SMR):
The ratio of the observed to the expected deaths due to cancer; the expected number is based on the age-specific mortality rates for all of Canada.

Statistical Significance:
A method that tests whether the result given is so rare that it is unlikely to be due to chance alone. Examples include a p-value (for probability) or a T-test. The most common cut-off is 5%, that is if this result would occur by chance only one in twenty times, it would be considered to be significant.

Surveillance:
Cancer surveillance includes the collection of data, and the review, analysis and dissemination of findings on incidence (new cases), prevalence, morbidity, survival and mortality. Surveillance also serves to collect information on the knowledge, attitudes and behaviours of the public with respect to practices that prevent cancer, facilitate screening, extend survival and improve quality of life.

Survival Rate:
The proportion of people diagnosed with cancer who are still alive after a given period, most commonly 1, 5 or 10 years after diagnosis.

Test for Trend:
A mathematical test that will help determine how likely an increase or decrease in incidence or mortality rates is greater than expected due to random chance.

Variation / Variability:
For given areas, how different the rates are from each other, or from the national value. Whenever you examine a large group of numbers, such as cancer rates across Canada, there will always be some variability in the numbers due to chance, some will be higher and some will be lower.


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Last Updated: 2005-04-12