# Prevalence and incidence relationship quizzes

### Block 9 Epidemiology Part 2 MCQ's - ProProfs Quiz

Incidence Quiz Incidence: Using Percentages to Measure Prevalence What is the incidence of part-time employment among female. Semester 3 Practice Questions In Epidemiology . Researchers investigated the relationship between the use of statins and prostate cancer. b) Incidence c) Calculation of person-time at risk d) Issues in defining the population at risk e) The relationships between incidence and prevalence f) Commonly.

Measure of risk B. Generally preferred for chronic diseases without clear date of onset A.

## Relationship Among Prevalence, Incidence Rate, and Average Duration of Disease

Used in calculation of risk ratio B. Affected by duration of illness Incidence reflects new cases only; incidence proportion is a measure of risk. A risk ratio is simply the ratio of two incidence proportions. Prevalence reflects existing cases at a given point or period of time, so one does not need to know the date of onset. Prevalence is influenced by both incidence and duration of disease — the more cases that occur and the longer the disease lasts, the greater the prevalence at any given time.

The relationship between prevalence and incidence The proportion of the population that has a disease at a point in time prevalence and the rate of occurrence of new disease during a period of time incidence are closely related [1]. The incidence rate r 2.

The duration of disease T For example, if the incidence of a disease is low but the duration of disease i.

For example diseases like leprosy or tuberculosis tend to persist for a longer duration, from months to years, hence the prevalence old and new cases would be longer than the incidence.

Conversely, if the incidence of a disease is high and the duration of the disease is short, the prevalence will be low relative to the incidence [1].

"Measures of Risk in Epidemiology".... Made Easy

For example, acute conditions like diarrhoea have a relatively short duration a few days. A change in the duration of a disease, for example the development of a new treatment which prevents death but does not result in a cure will lead to an increase in prevalence.

Fatal diseases or diseases from which a rapid recovery is common have a low prevalence, whereas diseases with a low incidence may have a high prevalence if they are incurable but rarely fatal and have a long duration. The relationship between incidence and prevalence can be expressed as: In such theoretical circumstances, the point prevalence of disease is approximately equal to the product of the incidence rate and the mean duration of disease i.

Other commonly used measures of disease frequency in epidemiology Measures of effect Measures of effect are used in epidemiological studies to assess the strength of an association between a putative risk factor and the subsequent occurrence of disease. This requires that the incidence of disease in a group of persons exposed to a potential risk factor is compared with the incidence in a group of persons not exposed to the potential risk factor.

• Lesson 3: Measures of Risk
• Semester 3 Practice Questions In Epidemiology
• Block 9 Epidemiology Part 2 MCQ's

This comparison can be summarized by calculating either the ratio of measures of disease frequency for the two groups or the difference between the two, and reflects the increase in frequency of disease in one population compared with another, treated as baseline. These measures are often collectively referred to as measures of relative risk The relative risk is a measure of the strength of an association between an exposure and disease and can be used to assess whether a valid observed association is likely to be causal [1].

The most commonly used measure of effect is the ratio of incidence rates that is: Rate or risk in exposed group Rate or risk in unexposed group 7.

Three main measures of effect Example: Duration is the average time that people have the disease from diagnosis until they are either cured or die. If the frequency of disease is rare i.

Similarly, if the incidence remained constant, then developing a cure would reduce the average duration of disease, and this would also reduce the prevalence of disease.

In the late s anti-retroviral therapy was introduced and greatly improved the survival of people with HIV.

### Principles of Epidemiology: Lesson 3 Quiz Answers|Self-Study Course SS|CDC

However, they weren't cured of their disease, meaning that the average duration of disease increased. As a result, the prevalence of HIV increased during this period. The relationship can be visualized by thinking of inflow and outflow from a reservoir.

The fullness of the reservoir can be thought of as analogous to prevalence.

Raindrops might represent incidence or the rate at which new cases of a disease are being added to the population, thus becoming prevalent cases. Water also flows out of the reservoir, analogous to removal of prevalent cases by virtue of either dying or being cured of the disease.

Imagine that incidence rainfall and the rate of cure or death are initially equal; if so, the height of water in the reservoir will remain constant.