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29 Cards in this Set
- Front
- Back
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What is epidemiology concerned with?
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the presence of health problems
the occurrence of new healthy events in a population and their quantification/measurement |
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What is a measure of disease?
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the amount of disease at one point in time or in a period of time
change in the amount of disease over a time period |
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What is the purpose of measuring diseases?
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to now what is going on in the population and how disease is changing in a population
-ID important diseases -Quantify disease risk in animals and their products compare disease in groups |
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When measuring a disease frequency what is important to define?
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What is being measured
the person or animals included in the measurement: the study population place of location of the study population Time period of the study |
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What are considerations in planning a measure?
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carefully define the study population
clarify relationships between the numerator and denominator for the calculation of rates and ratios identify potential associations between outcome and the factors being studied -is one gender more likely to be affected -does rate of disease differ by geographical location |
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What are the most common types of measures?
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-count
-proportion -rate -ratio |
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What is a count measure?
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absolute number of animals that have a particular disease
-26 horses from St Kitts had evidence of expose to babesia caballi all other measures of disease occurance are based on counts |
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What is a proportion measure?
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the count of diseased animals expressed as a fraction of the animals that could be diseased
- # of dz animals/ # animals in the study carried out in a percent |
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What is a rate measure?
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an expression of change in the amount of disease in a defined population per unit time
- # of new occurrences of diseases/ # the number of animals in the study |
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What is a ratio measure?
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a fraction in which the numerator is not a part of the denominator
for every part of the one thing how much is there of another thing 6 ticks/1 Sheep |
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What is prevalence?
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the proportion of the study population that is diseased at any one time
a measure of the amount of disease in the population at any one time interpret as the probability of being diseased |
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What is point prevalence?
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the proportion of the study population that is diseased at a single point in time
the most common measure of prevalence is often determined by cross-sectional studies and surveys interpret as the probability that an individual in the study population is diseased at the time of the study |
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How do calculate point prevalence?
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number of cases of disease present in the population at a particular time/ total population at that specific time
expressed as a percent, portion or fraction |
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What period prevalence?
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the proportion of the study population that is diseased during a specific period of time
measures all the cases of disease in the study population over a period of time includes old cases that were present at the beginning and new cases the probability that an individual in the study population is diseased during the period under study |
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How do you calculate period prevalence?
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number of cases of disease present in the population over a period of time/ total population over that period time
expressed as an express, proportion # diseased/ 1000 pop/ time period |
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What is incidence?
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the number of new causes of disease in a population observed over time
how frequently susceptible individuals become diseased over time only counts new cases of disease incident cases are new cases of disease -the probably of a susceptible individual becoming diseased use to predict disease occurrence |
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What is cumulative incidence?
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the proportion of disease free individuals in a population who became diseased during the specified period of time
includes only susceptible individuals in the study population at the beginning of the study includes new cases of disease that develop over the time period of the study -the probability of a susceptible individual becoming diseased during the study period |
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How do you calculated cumulative incidence?
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new cases of disease or events during the time period/ total population at risk at the beginning of the time period
epressed as a number with reference to time and the pop at risk as a percent |
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What are assumptions of cumulative incidence?
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all individuals in the study are at risk of the outcome of interest
every individual is assesssed at the beginning to identify and remove old cases entire population at risk must be followed from the beginning of the study till the end |
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What is an attach rate?
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cumulative incidence during an epidemic
applied to a narrowly defined population observed for a limited period of time -the probability of becoming diseased during the course of an epidemic |
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How do you calculated attack rates?
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# of new cases of illness during a specified time period (epidemic)/ total population at risk (exposed) during that specified period (epidemic)
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What is incidence density(rate)?
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instantaneous rate of occurrence of new cases of diseased among susceptible animals in the population
use when animals are entering and leave the pop during the study numerator is the number of new cases of disease during the study period the denominator is calculated by adding together the number of time units that each at risk individual in the population was observed |
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How do you calculated incidence density (rate)?
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# of new cases of disease during the study / sum of the length of time during which each individual in the population is at risk
reported as animal time period prevalence and cumulative incidence are reported as cases/ animals / time |
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prevalence vs incidence?
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P: a measure of the amount of disease in a population
-all cases (old and new) -estimates probability animal is diseased I: a measure of the rate of disease occurrence -includes only new cases used for disease management, estimate number of cases of disease that are expected to occur in the next time period |
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What factors increase prevalence?
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-longer duration of disease
-prolongation of life without a cure -increase in new cases -in migration of cases -out migration of healthy animals |
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What factors decrease prevalence?
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-short duration of disease
-high case-fatality rate from disease -decrease in new cases -in migration of healthy animals -out migration of cases -improve cure rate |
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What are Mortality rates?
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the incidence of death in a given time period
number of deaths during the time period/ total population during that time |
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What is cause specific mortality rate?
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due to a specific disease or event
number of deaths from a specific disease/event/ total population during the same time |
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What is a case fatality rate?
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the number of cases that are fatal withing a specified time following disease onset or diagnosis
number of individuals cases of disease that die/ total number of individuals with the disease |
