# Epidemiology& Veterinary Public Health

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- Created by: Grace Thoroughgood
- Created on: 15-02-16 12:43

Public Health

Public Health is the sum of all contributions to the complete physical, mental and social wellbeing of humans through an understanding and application of veterinary medical science.

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Medical Epidemiology

Clinical observations acknowledging importance of circumstances and environment of cases

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Demographic epidemiology

Use of death counts and comparison of rates

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Theoretical epidemiology

Theories about spread of epidemics- before recognition of micro-organisms as a cause of disease

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Zoonoses

Diseases transmitted between animals and humans

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Epidemiology

Study of diseases at the population level in a systematic way, involving the formulation of hypothesis which are tested on the basis of experimental or observational data

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Endemic Occurence

Usual or constant presence of disease in a population

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Epidemic Occurrence

Occurence of a disease to a level in excess of the expected (i.e. endemic) level

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Sporadic Occurrence

Single cases or clusters of cases of disease which are normally not present in an area. The disease occurs irregularly and, in general, not frequently

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Veterinary Epidemiology

The study of disease, productivity and welfare in animal populations. Holistic approach to animal health and disease. Measure two elements: exposure and outcome.

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Necessary causes

must be present for a disease to occur

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Sufficient causes

set of minimal conditions and events inevitably producing disease.

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Counts

number of individual animals which are infected, diseased or dead

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Fractions

number of individual animals which are infected,diseased or dead/number of animals capable of experiencing infection, disease or death.

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Ratio

the relative size of two quantities expressed by dividing one by other e.g. a/b

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Proportion

a ratio whose numerator is included in the denominator e.g. a/a+b

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Rate

A ratio that represents the magnitude of change in the occurrence of an event of interest e.g. infection, disease, death) with respect to a population at risk over time

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Prevalence

The total number of individuals who have a disease at a particular time divided by the population at risk of having the disease.

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Incidence

The number of new cases of a disease that occur in a defined/population within a specified period of time.

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Cumulative incidence

Proportion of disease-free individuals developing a given disease over a specified period of time. Dimentionless. Ranges from 0-1. Always requires a period referent.

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Incidence density

instantaneous potential for change in disease status per unit time at time t, relative to the size of the disease free population at time t. Number of new cases/population time at risk

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Attack rate

Number of new cases/initial population at risk. It is a subtype of cumulative incidence (despite its name a probability, not a rate) used when the period at risk is short.

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Crude mortality rate

Analogous to incidence density with death due to specific causes as the outcome of interest.

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Case specific mortality rate

Analogous to incidence density with death due to specific causes as the outcome of interest.

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Case fatality rate

Animals dying for a specific condition/Animals with the condition (despite its name it is a probability not a rate). It is used to describe the impact of epidemics or the severity of acute diseases.

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Field studies

Conducted in the animals natural environment. Animals exposed to all environmental influences including both known and unknown factors. Highly relevant to clinical practice.

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Clinical Trials

Systematic studies conducted in order to establish the effects of prophylactic or therapeutic procedures

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Reference Population

Population that will benefit if the treatment is effective.

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Study population

Population in which the trial is conducted

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Type 1 error

declaring a difference where none exists

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Type 2 error

declaring no difference where a meaningful one does exist

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Simple Randomization

e.g. tossing a coin. Should be undertaken after eligible units have been identified. Normally done using random numbers.

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Block Randomization

Randomization is done within blocks of units to ensure that within a block of N animals the same number of subjects are allocated to each treatment.

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Selection Bias

Animals included in the trial systematically differ from animals not included. To avoid: Appropriate selection of reference and study population and random allocation.

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Confounding Bias

A risk factor for the outcome is also associated with the treatment. To avoid: random selection of the treatments

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Information Bias

Information on the different outcomes is recorded in a different way for treated and non-treated animals. To avoid: Blinding.

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Censoring Bias

When there is differential follow up across time for subcohorts, and the reason for censoring is a determinant of the outcome. Ensuring equal follow up in both groups.

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Cross sectional studies

Studies in which data on the factor and outcome of interest in the population being studied are recorded at the same time. Individuals are selected without regard to exposure or disease status.

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Cohort Studies

Studies in which two or more groups within a population are defined according to their exposure or non-exposure to a risk factor of interest and followed through time to determine the frequency of occurrence of the outcome of interest

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Risk

Probability that an event will occur at a given time during a given period.

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Risk factor

Factor associated with an increase in the probability of occurence of an outcome of interest.

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Prediction

Estimating the likely future frequency of disease among comparable individuals

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Diagnosis

Presence/absence of a risk factor increases/decreases the likliehood that disease is present

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Causality

In some cases, risk factors are causally associated with the condition

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Prevention

Reducing the exposure to the risk factor can be used to prevent disease, even if the disease mechanism is unknown.

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Precision

Degree of fluctuation of a test series based on a sample around a central measurement.

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Gold Standard

Means by which one can assess whether a disease, or any other event of interest, is truly present or not

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Predictive Values

Probability that a test for a particular animal correctly identifies the condition of interest.

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Positive Predictive Value

Probability that an individual found positive to a test is truly affected by the disease or outcome of interest

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Negative Predictive Value

Probability that an individual found negative to a test is truly free of the disease or outcome of interest

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ROC Analysis

Description of the performance characteristics of a diagnostic test (Sensitivity and Specificity) for the different cut-offs (operating conditions).

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Specificity

Ability of a test to correctly detect individuals free of the disease or infection of interest.

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Sensitivity

Ability of a test to correctly detect individuals with the disease or infection of interest.

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True Prevalence

Based on the true disease status of the individuals.

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Apparent Prevalence

Estimate of the prevalence based on the means used to identify disease.

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## Other cards in this set

### Card 2

#### Front

Clinical observations acknowledging importance of circumstances and environment of cases

#### Back

Medical Epidemiology

### Card 3

#### Front

Use of death counts and comparison of rates

#### Back

### Card 4

#### Front

Theories about spread of epidemics- before recognition of micro-organisms as a cause of disease

#### Back

### Card 5

#### Front

Diseases transmitted between animals and humans

#### Back

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