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157 Cards in this Set
- Front
- Back
How would you define epidemiology?
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Study of the occurrence of disease in a population, and the factors that influence disease occurrence and distribution
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How is population defined?
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The totality of individuals of the same kind that share common attributes
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True or False. The underlying premise of epidemiology is that disease is random.
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False
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The process of epidemiology includes what 3 steps in studying health problems?
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Detected
Investigated Analyzed |
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The uses of epidemiology include the description of disease occurrence in populations and the study of what type of factors that predispose to disease?
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Causal factors
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The information gathered from epidemiological studies is used to do what?
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-Research new methods for the investigation and control of disease
-Manipulate possible causal factors to reduce disease occurrence and productivity loss |
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Macroepidemiology address issues at which level?
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Global ,international levels (pandemics)
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Which type of epidemiology addresses national issues?
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Microepidemiology
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Which branch of epidemiology studies the disease risk with the presence of susceptibility genes?
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Molecular epidemiology
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Genetic epidemiology focuses on causal factors of what type?
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Genetic
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The use of technologies such as IFA to detect disease, falls under which branch of epidemiology?
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Seroepidemiology
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The study of the distribution of disease as measured by incidence and prevalence is what branch of epidemiology?
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Descriptive
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Analytical epidemiology is the study of what components of disease?
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Determinants of disease such as causal factors using relative risk and odds ratios
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Evidence based vet med relies on good clinical trial data and clinical knowledge based on what type of data?
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Population data
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How does the epidemiologist indentify the cause of a disease?
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-Finds assoc. between factors & disease
-Infers possible causal factors -Descriptive data of disease in populations -From observation to prevention of disease |
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The usual (constant) frequency of disease in a population is the definition of what?
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Endemic
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What is the definition of epidemic?
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Occurrence of disease in excess of expected level
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What is another term for edemic?
For epidemic? |
Edemic- enzootic
Epidemic- epizootic |
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What type of widespread epidemic involves more than 1 country?
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Pandemic
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How do you define sporadic disease?
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Irregular, haphazard occurrences
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The onset of disease my be reported..
-in time -by time series analysis and what other 2 ways? |
-By host related distribution
-By space |
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Endemic disease occurs at what frequency?
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-Expected, usually low and predictable
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How are epidemic disease occurrences shown graphically?
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Epidemic curves
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Name the 3 types of epidemic curves
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-Point source
-Continuous, common source -Propagating epidemic |
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The point source curve represents what type of epidemic?
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Large number of cases in a short period of time
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An epidemic in which exposure to the source is prolonged over an extended period of time results in what type of curve?
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Continuous common source epidemic
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What is a propagating epidemic?
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When a case of a disease serves as the source of infection for subsequent cases.
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Disease that occurs in a small number of cases over a short period of time is usually called what?
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Sporadic disease
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A time series analysis of disease serves what purpose?
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Identify periods of high or low risk so that causal associations can be explored. Detects temporal trends of a disease.
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A secular time series analysis show disease incidence occurring over a long or a short time period?
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Long time period
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Changes in disease incidence rates over periods of less than 1 year are called what time of time series analysis trend?
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Seasonal
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The rise and fall of disease occurrence over a period of greater than 1 year is called what type of trend?
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Cyclical
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Irregular trends reflect what type of occurrence variation in populations?
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Random
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Host distribution means that disease occurrence is categorized by what?
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Host factors such as age, sex, breed
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What is the definition of incidence?
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Number of new cases occurring in a population over a defined time period
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How is incidence usually expressed?
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As number per unit of population at risk
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How are new cases identified?
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Often not possible, screen the population for baseline rate, then those without disease are followed for 1 year then re-screened
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What is the definition of prevalence?
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Number of cases present at any given time
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How is prevalence usually expressed?
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As a proportion between 0 and 1 or as a % or as a number per unit of population
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What is point prevalence?
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Prevalence at a point in time
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What is period prevalence?
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Number of people that have had the diesease during a certain period of time i.e. a calendar year
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Does period prevalence take into account the duration of the disease?
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No
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In a steady state situation, what is the relationship between prevalence and incidence?
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Prevalence = Incidence X Duration
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A change in prevalence can be due to what?
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-A change in incidence rate
-Change in duration of the disease -Change in both |
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Knowing the prevalence of a disease can help with what?
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-Interest in existing cases of disease
-Identify major disease problems -Identifying/evaluating control strategies (vaccinations, de-worming) |
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Knowing the incidence of disease can do what?
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-Predict population's health status
-Assess the probability that an animal within a population may develop a disease of interest |
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What is meant by the term Attack Rate?
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Measure of the proportion of the population that develops disease among the total exposed at the start of an outbreak
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What is involved in the process of data visualization?
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Plotting data on a map to look for meaningful patterns
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What is meant by cluster analysis of spatial distribution?
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Measure of disease occurrance in time and space
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What is data modeling used for?
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Used to test hypotheses and plan health policies
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Who developed the concepts of identifying cause-effect relationships?
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Evans
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Causal factors are grouped into what 3 categories?
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-Disease agents
-Environmental influence -Host factors |
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What are some disease agents?
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Bacterium, virus, non-living causes (temp)
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What is meant by the term infection?
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The ability of an agent to establish itself in a host
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The ability of an agent to produce disease in a range of hosts is the definition of what term?
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Pathogenic
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What is virulence?
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A measure of the severity of disease caused by the agent
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What is indicated by a non-statistical association between a cause and a disease?
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Arises by chance
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What is meant by a statistical association?
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Variables (disease and possible cause) are statistically more (or less) frequently associated than due to chance
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A statistical association is significant only if a statitistical test shows what type of significance?
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95% to 99% probability that the association is not due to chance.
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Risk factors can cause disease or....
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Increase the likelihood of developing a disease.
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In terms of causal factors, a dose of a virus required to cause a disease is considered to be necessary and...
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Sufficient
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When multiple factors are needed to cause a disease, each factor is said to be what?
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Necessary but not sufficient
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A dose-response relationship between a cause and a disease shows what association?
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Varying amounts of the suspected cause are related to varying amounts of effect
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The mechanisms of a disease have what type of basis?
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Biological
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Which type of study design is the strongest n terms of showing evidence for a causal relationship?
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Clinical trial
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What 2 measurements measure the strength of the association between cause and effect?
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Relative risk
Odd's ratio |
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What factors can impair making a causal inference?
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-Lengthy time interval between cause and effect
-Multiple causes leading to same effect -Causal factor requires other factors for effect |
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What is selection bias?
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Any error that arises in the selection of the study population
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What is surveillance bias?
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Assessment of disease my be better in the monitored population
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When people/animals are grouped incorrectly, this is called what type of bias?
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Misclassification bias
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A misclassification of the disease is called what?
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Differential misclassification
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Putting diseased animals into a control group is what type of misclassification?
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Non-differential misclassification
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The way in which information is extracted from medical records could be subject to what type of bias?
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Information bias
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Bias must be eliminated at which stage of a study?
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At the commencement
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How is bias controlled?
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Through careful study design, and careful choice of population, methods of data collection
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What is confounding?
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Distortion or masking of an association between an exposure and an outcome (disease) because of a third factor
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The confounding factor must be associated with the exposure (risk) factor, and be what with the risk factor for the disease?
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Independent
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What 3 design controls can help minimize confounding?
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-Radomization
-Matching -Restriction |
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During the analysis of a study, confounding can be minimized by what 2 approaches?
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-Stratification - evaluate association within subgroups
-Multivariate analysis - takes into account many variables at one time |
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Descriptive studies describe patterns of disease according to what 3 components?
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-Where
-Who -When |
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What are the benefits to descriptive studies?
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-inexpensive
-used when little is known about a disease -less time-consuming -easy to collect info |
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Descriptive studies usually lead to what?
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A hypothesis that is then tested
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The description of a since case or groups of cases is what type of descriptive study?
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Case Reports (case series)
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What is a big weakness of case reports?
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No comparison (control) group
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A cross-sectional study is also called what?
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Prevalence study
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What does a cross-sectional study describe?
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a snapshot at any defined point in time
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What is a weakness of cross-sectional studies?
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-cannot assess cause and effect
-may miss expsoures that vary over time |
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Cross-sectional data is place into what type of table for analysis?
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2 x 2
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Descriptive studies that evaluate disease on a group level are called what?
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Ecologic or correlational
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What is a ecological fallacy?
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If an assumption is made that the association found at the herd/group level is also true on the individual level
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True or false. Ecological studies can indicate a causal hypothesis, but cannot determine the cause of a disease
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True
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What is a cohort?
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A group of person's sharing particular statistical or demographic characteristics
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When is a cohort study usually done?
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After a hypothesis is formed from a case control study
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A cohort study starts with identifying the exposed cohort and the non-exposed cohort, and then measuring what?
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Disease occurrence in each and compare
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Prospective cohort studies follow-up disease from where to where?
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From present to future
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Retrospective cohort studies follow-up disease from where to where?
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From past to present
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What are the strengths of cohort studies?
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-can directly measure incidence
-useful when exposure is rare -can exam multiple outcomes of a single exposure -can describe temporal relationships -can collect data on possible confounders (prospective) |
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What is a weakness of cohort studies?
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Inefficient for rare disease, need to follow large cohort for a long time
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What are risk factors?
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Any factor associated with an increased risk of becoming diseased or to die
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The relative risk (risk ratio, RR) is used to answer what question?
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How much more likely are exposed individuals to get the disease relative to non-exposed individuals
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How do you interpret an RR close to 1?
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Close 1 means that the exposure is probably not associated with risk of disease (greater or smaller than 1, the exposure is associated with disease)
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How is the RR calculated?
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Incidence in exposed/Incidence in non-exposed (I 1/I 0)
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True or false. Knowing the Relative risk (RR) also gives you statistical significance.
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False
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What value is used to give statistical significance?
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Confidence interval
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What implication does a 95% confidence level that includes 1, have?
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The finding could be due to chance, the result is not statistically significant
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A case control study starts with what information?
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Disease, as opposed to exposure
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In a case control study, control groups are selected from where?
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From the defined population
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In a case control study, what calculation is used to estimate relative risk?
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Odds ratio (AD/BC)
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When are case control studies used?
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-When a disease is rare
-When there is a long time interval between exposure and outcome |
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Non-observational, clinical trials are used to evaluate what?
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Therapeutic or preventative effects of particular interventions, and etiologic relationships
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Groups or subjects, or animals are divided into what 3 groups for a clinical trial?
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-A treated control group
-Untreated control group -Placebo controls |
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what do therapeutic trials assess?
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Test the agent or procedure to dimish symptoms, prevent recurrence or reduced risk of disease or death
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What type of trial evaluates whether an agent or procedure reduces the risk of disease in those currently free of disease?
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Prevention trials (field trial)
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Trial may be of what 3 design types?
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-Open
-Blinded -Double blinded |
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What are the strengths of clinical trials?
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-Researcher has control over the study situation
-Large sample size and design eliminates unwanted factors -Use of blinding to eliminate bias -Provides cause-effect data -Randomization minimizes confounding |
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What is the use of a screening test?
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Indentify individuals that may have a particular disease
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For a screening test to be valid, it must be able to do what?
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Distinguish those that have the disease from those that don't
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In terms of a screening test, what is meant by sensitivity and specificity?
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Sensitivity- correctly identifies those that have the disease
Specificity- correctly identifies those that do NOT have the disease |
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In a screening test, what are false positives.
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People who do not have the disease are are erroneously called positive by the test
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What is the predictive value of a screening test?
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If the test is positive, what is the probability that the animal does HAVE the disease?
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How does prevalence affect the predictive value of a screening test?
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The higher the prevalence of disease, the higher the predictive value
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What factors can affect the reliability (affect the variation) of a screening test?
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-Intrasubject variation
-Interobserver variation |
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What is screening?
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The examination of asymptomatic animals in order to classify them as likely/unlikely to have the disease
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Why do we screen?
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To reduce morbidity and mortality attained by early treatment of cases discovered by screening
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When is screening most useful?
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When a disease can be detected during its pre-clinical phase
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What is the biologic onset of disease?
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The point at which there may be a sub-cellular change in the DNA, but no symptoms of disease
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What is the term for the time from the onset of disease until clinical signs/symptoms?
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Preclinical phase
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Signs of disease develop during which phase?
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Clinical phase
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To evaluate a screening test, what 2 types of study designs are used?
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Non-randomized (such as cohort)
Randomized |
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What is the disease incubation period?
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Time between exposure to an agent and onset of clinical signs/symptoms of disease
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What is extrinsic incubation period?
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Used with vector-borne diseases, time period the agent requires in a vector before it is capable of inducing infection in the next host the vector encounters
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What is the term for the period between the intial infection of the host and when the host becomes infectious to others?
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Latent period
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What is the period of transmission?
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Agent is being shed by the host
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What factors affect the transmission of a disease?
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-agent
-host -reservoir -vector |
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What is a reservoir?
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The habitat in which the agent resides and propagates (can be animate or inanimate)
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What is an essential or reservoir host?
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A host that is required for maintenance and multiplication of the agent
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What is the term for the host in which the agent multiplies to high levels, sufficient to spread to other hosts?
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Amplifier host
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What type of host is not reuqired for maintenance but can become infected with the agent>
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Accidental host
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What is a dead end host?
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A host that cannot spread the infection to other susceptible hosts under natural conditions
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What is a mechanical vector?
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A vector in which there is no development of the pathogen, the agent is mechanically carried
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What type of vector does have replication/development of the pathogen?
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Biological vector
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name the 3 modes of vertical transmission.
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-Tranplacental (in utero)
-Perinatal -Postpartum |
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What is the definition of infection?
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Encounter of a potentially pathogenic agent with a susceptible human/animal host that shows an immunologic response to infection
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What is meant by the carrier state?
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The individual sheds the organism but is usually not infected
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Description of the occurrence of infectious disease includes what 4 points?
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Who
Where When What |
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"Who" includes the host factors, what does "When" include?
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Seasonal variation
Secular variation (over prolonged time) |
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The "What" of disease occurrence describes which aspects of the disease?
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Infectivity
Pathogenicity Virulence Immunogenicity |
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What is meant by attack rate?
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# of new cases for epidemic period
______________________________ population at risk |
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What is a secondary attack rate?
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Person to person transmission of infection
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How is the secondary attack rate usually measured?
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In households or schools
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What is pathogenicity?
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Ability of an agent to induce a disease
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What is virulence?
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Ability of an agent to induce severe or fatal disease
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How is the case fatality rate calculated?
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# fatal cases / # total cases
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How is the mortality rate calculated?
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# of deaths in the population /
# of individuals n the total population |
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What is immunogenicity?
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Ability of an agent to induce an immune response (as measured by antibody production)
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What is herd immunity?
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Resistance of a group, community or population to the introduction and spread of an infectious disease, based on the collective immunity of the group
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How can herd immunity be gained?
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Naturally or by vaccination
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