A Guide to HIV/AIDS Epidemiological and Surveillance Terms

[Previous] [Table of Contents] [Next]

Frequently Used Terms in HIV/AIDS Monitoring and Epidemiological Research in Canada

RANGE

The range is an example of a descriptive statistic. The range describes the spread of scores. The range is the highest value minus the lowest value in any set of values.

RATE
(See also RATIO)

A rate is an expression of the frequency with which an event occurs in a defined population in a specified period of time. In HIV/AIDS research, a rate can be the proportion of a population with a particular "event", such as HIV infection, occurring during a specified time period.

A rate can be obtained by dividing the number of cases in a given time period by the population at risk in the same time period and then usually multiplying the result by a multiple of ten. In epidemiological reports, 100,000 is commonly used as this number (the multiplier). The rate can then be expressed as the number of people with the "event" per 100,000 population. Expressing the rate as the number of people per 100,000 per year is done so that rates can be compared between population groups and from year to year.

You can compare rates between different populations as long as the rate has been calculated using the same multiplier.

RATIO

A ratio is a combination of two numbers that shows their size relative to each other.

The ratio of one number to another is the first number (the numerator) divided by the other number (the denominator), and can be expressed as a fraction or a decimal. A ratio can also be expressed as two numbers separated by a colon (:).

REPORTABLE DISEASE
(Refer to NOTIFIABLE DISEASE)

REPORTED AIDS CASES
(See also AIDS CASE REPORT and FAQs 6, 8, 14, 16, 17)

Reported AIDS cases are those AIDS cases on which information about the individual has been sent to the provincial or territorial government and then reported to the Centre for Infectious Disease Prevention and Control (CIDPC).

It is important to note that the number of reported AIDS cases at any point in time is not a true reflection of the total number of AIDS cases that have been diagnosed in Canada since the beginning of the epidemic. This is because some AIDS cases never get reported for a variety of reasons, such as health care providers being unaware of the legal requirement to report AIDS cases. You will often see this situation referred to as "under-reporting".

Also, there are often substantial delays in reporting AIDS cases. It is currently estimated that 23% of newly diagnosed AIDS cases are reported to CIDPC within three months, 45% within six months, 65% within one year, 82% within two years and 95% within five years. You will often see this situation referred to as "delayed reporting".

RISK FACTOR
(See also FAQ 3)

A risk factor is an aspect of someone's behaviour or lifestyle, a characteristic that a person was born with, or an event that he or she has been exposed to, that is known to be associated with a health-related condition.

A behavioural risk factor describes a specific behaviour that carries a proven risk of a particular outcome. In HIV/AIDS research, you will often see the term "HIV-related risk behaviour" to describe a behaviour that, when practiced, carries a proven risk of HIV infection.

An individual's HIV-related risk factors determine the exposure category assigned to a report of a positive HIV test.

[Previous] [Table of Contents] [Next]