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30 Cards in this Set
- Front
- Back
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define Incidence and give the formula
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The instantaneous per capita rate of disease onset
1/Average age of onset = True Incidence Number of new cases of disease that occur in a defined population over a specified period of time also i = C/R where C = number of animals sick and R is the sum of the months that an animal survived without being sick |
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Case/Control
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Case persons diagnosed with disease
Controls: similar group of people without disease |
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Counting cases
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ONly if the population size stays constant
constant fraction of the population is sampled |
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Define Prevalence
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proportion of the population that has the disease at one specific point in time
C/(C+R) where C is current number of cases and R is the current number at risk of disease prevalence = i*D/(1+i*D) D = Duration of disease (1/D = recovery rate) |
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Cohort Studies
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They are used to test hypothesis about causation
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Endemic Model
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Dx/dt = mu*N-BetaXY-mu*X
Dydt = Beta*x*y-lambda*Y - mu*Y Dz/dt = lambda*Y-mu*Z mu = instantaneous per capita birth/death rate lambda = instantaneous per capita recovery rate Beta = transmission coefficient X = density of susceptible hosts, Y = density of infectious hosts Z = density of recovered/immune hosts Basic Reporduction: Beta*N/(mu + lambda) Population Specifc Beta*X/(mu + lambda) |
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Define Effect
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difference in disease occurrence between two groups which differ with respect to a particular exposure
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Risk
Relative Risk |
Risk = Cases / numbers at start
Relative Risk = CumI in exposed group/ CumI in unexposed group |
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Randomization
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Eliminate known and unknown sources of bias
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Selection bias
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animals not randomized with respect to treatment with topical flea control product
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Validty
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Extent to which a study measures what is suspposed to measure
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Bias
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Systematic Error
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Information Bias
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Systematic error that occurs during the collection of information after enrollment (misclassification and Recall Bias)
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Recall Bias
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colicky horses remembered the exposures more thoroughly than owners (people remember sick)
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Misclassification Bias
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Non-differential = moves OR/RR towards 1
Differential = OR or RR away from 1 |
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Spectrum Bias
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Unable to generalize and understand components
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p-value
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p-value is a rough guide to the compatibility between the data and the null hypothesis
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Confidence Interval
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rough guide to and a minimum estimate of the inherent uncertainty of the study results
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Confounder
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It must increase or decrease the incidence of the disease and it must be associated with the factor whose effect you think you are measuring
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Disease is rare
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RR = OR
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Model for SIR
S-(Beta*I)->I -(alpha)-(lambda)->R |
Ds/dt = -Beta*I*S
dI/dt = Beta*I*S - alpha*I - lambda*I dR/dt = lambda*I |
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Ro = 1 + L/A
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L = is average life expectancy
A = average age at infection |
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Eliminating the infection
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p = 1 - 1/Ro
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Surveillance
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generate Policies, Generate hypotheses, monitor effectiveness of control programs, health status of population
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Passive Surveillance
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attention because they are suspected of being cases
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Active surveillance
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Examine animals to detect sub-clinical and carrier animals
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Power
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Probability of detecting a difference between the treated grup and the control group when a different actually exists
power = 1 - Beta |
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Prognosis
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prediction of the expected outcome with or without treatment
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epidemic
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occur when the incidence of disease increases beyond that considered normal for the area
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endemic infectious disease
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where it has persisted there for a long time
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