Epidemiology chp 2
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-the review of data for accuracy and completeness
-A clean data set contains a group of data that are ready for coding and analysis
•Is a type of graph that shows the frequency of cases for categories of a categorical (discrete) variable such as a Yes/No variable.
a similar chart to bar chart, used for continuous variables
-A variable that could have an infinite number of values along a continuum.
- -Ex. height, weight, and blood sugar level
- -Cannot be anwsered with yes/no
-Used to display trends, e.g., time trends
A circle that shows the proportion of cases according to several categories
- The value obtained by dividing one quantity by another.
- Examples are:
- With respect to AIDS mortality, the sex ratio of deaths (male to female deaths) = X/Y, where:
- ─X= 450,451
- ─Y= 89,895
- The sex ratio = 450,451/ 89,895 = 5 to 1 (approximately).
•A type of ratio in which the numerator is part of the denominator
•May be expressed as a percentage
•A proportion that has been multiplied by 100.
- •The formula is (A/A+B) X 100.
- •From the previous slide:
- –The percentage of male deaths from AIDS was (0.83 X 100) = 83%.
Also a type of ratio, a rate differs from a proportion because the denominator involves a measure of time
General Information Regarding Epidemiologic Measures
- provide the following types of information:
- ─frequency of a disease or condition
- ─associations between exposures and health outcomes
- ─strength of the relationship between an exposure and a health outcome
Quantitative Epidemiologic Measures
- characterize the occurrence of disease, morbidity, and mortality in populations.
- Quantitative terms include: Counts, Incidence, Prevalence
- number of cases of a disease or other health phenomenon being studied.
- • single cases may have public health significance
- ─Case reports of patients with particularly unusual presentations or combinations of symptoms often spur epidemiologic investigations.
- ─Ex one case of Ebola virus
occurrence of new disease or mortality within a defined period of observation (time period) in a specified population.
Population at Risk
members of the population who are capable of developing the disease or condition being studied are known as the population at risk.
A rate formed by dividing the number of new cases that occur during a time period by the number of individuals in the population at risk
- Number of existing cases of a disease or health condition, or deaths in a population at some designated time.
- •Variations: Point prevalence and Period prevalence/Lifetime prevalence
- •All cases of a disease, health condition, or deaths that exist at a particular point in time relative to a specific population from which the cases are derived.
- Point prevalence = Number of persons ill at a point in time
- Total number in the group
All cases of a disease within a period of time
- Cases diagnosed at any time during the person’s lifetime
- •Ex: Lifetime asthma diagnosis
Interrelationships Between Incidence and Prevalence
- Factors that cause prevalence to increase:
- ─Increase in incidence
- ─Longer duration of the case
- ─In-migration of cases
- ─Prolongation of life of patients without a cure
- •Factors that cause prevalence to decrease:
- ─Decrease in incidence
- ─Shorter duration of disease
- ─In-migration of healthy people
- ─Improved cure rate of disease
- •A type of rate that has not been modified to take account of any of the factors such as the demographic make-up of the population that may affect the observed rate
- •Includes a time period during which an event occurred.
- •Numerator consists of the frequency of a disease over a specified period of time.
- •Denominator is a unit size of population.Aid in making comparisons but have limitations
Crude Death Rate
- •The crude death rate is a type of crude rate.
- •Can be expressed in terms of any unit size of a population that is convenient.
- ─For example, infant mortality is expressed per 1,000 live births.
- •The population from which cases of a disease have been taken
- •Ex: calculation of the annual crude death rate in the United States
Case Fatality Rate (CFR)
- The number of deaths due to a disease that occur among persons who are afflicted with that disease=
- Number of deaths due to disease “X” Times 100during a time periodNumber of cases of disease “X”
Proportional Mortality Ratio (PMR)
The number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population
- A measure that refers to mortality (or frequency of a given disease) divided by the population size at the midpoint of a time period times a multiplier.
- Mortality (or frequency of a given disease) X 100,000
- Population size at midpoint of time period
•The number of cases per age group of population during a specified time period
- The frequency of a disease in a gender group divided by the
- total number of persons within that gender group during a
- time period times a multiplier
- •A rate of morbidity or mortality in a population in which statistical procedures have been applied to permit fair comparisons across populations by removing the effect of differences in the composition of various populations
- •Age is a factor used in rate adjustment.
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