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ACVPM > Epidemiology and Biostats Pt. 1 > Flashcards

Epidemiology and Biostats Pt. 1 Flashcards

1
Q

Prevalence

A

number of animals in a population at one point in time that have a particular disease (a proportion)

high prevalence means that risk is high and/or disease is chronic

low prevalence means risk is low and/or animals die or recover quickly

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2
Q

Three types of prevention

A

1) primary (preventing exposure to causal factors; quarantine and vaccination)
2) secondary (screening tests to detect dz before it occurs)
3) tertiary (treatments once you have the dz)

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3
Q

Rates vs. ratios vs. proportions

A

Rates = a/a+b over TIME
(the frequency with which an event occurs in a defined population in a period of time)

Ratios = a/b where a is not part of b
(the relative magnitude of 2 quantities or a comparison of any 2 values)

Proportions = a/a+b but no time element
(number of events with a particular characteristic/total number of events in which the numerator is a subset)

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4
Q

How close a test measures the truth

A

validity

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5
Q

precision vs. accuracy

A

precision = repeatability
accuracy = overall proportion of correct tests over total predictions

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6
Q

if you drop a titer from 1:100 to 1:50, the test becomes more:

A

sensitive

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7
Q

what is vehicle-borne transmission?

A

through inanimate objects (fomites)

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8
Q

time between exposure and maximum infectivity

A

generation time

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9
Q

exposure time to onset of illness

A

incubation time

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10
Q

first case that brought attention to the outbreak

A

index case

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11
Q

incidence

A

number of new cases in a population specific time
-usually expressed as a proportion or rate with a denominator: the probability of occurrence of a given condition in a population within a specified period of time (ie. 5 cases/10,000/year)

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12
Q

attack rate =

A

number of new cases/number exposed
ie. 5 people got sick out of 100 people who ate the salad

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13
Q

secondary attack rate =

A

of new cases occurring within the incubation period following ID of index case in a household, family or close contact / the susceptible # of persons exposed to the index case during the same time interval

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14
Q

crude mortality rate

A

proportion of individuals in a pop that die in a given period of time (usually expressed as a number per 1,000, 10,000…)

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15
Q

specific attack rate

A

number of cases in a defined subgroup

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16
Q

case fatality rate

A

cumulative incidence of death in the group of individuals that develop dz over a time period. Number of deaths of those that have the disease.

ie. 30 puppies died of parvo of 100 that were diagnosed = 30% case fatality rate

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17
Q

proportionate mortality rate

A

deaths by specific cause / deaths from all causes

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18
Q

Mean

A

the arithmetic average.
-sensitive to outliers

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19
Q

Mode

A

the most frequently reported observation

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20
Q

median

A

the observation result that has as many observations above and below when ranked in order

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21
Q

morbidity rate

A

number with disease / number at risk

22
Q

confidence interval

A

range of values that has a probability of containing the parameter being estimated
-width of CI indicates amount of variability inherent in the estimate and thus the effect of sample size
-increases as data becomes more variable
-gets tighter as sample size increases
-95% and 99% most commonly used

23
Q

odds ratio

A

a measure of association between an exposure and an outcome in a case-control study. Represents the odds an outcome will occur given a particular exposure, compared to the odds of an outcome occurring in the absence of that exposure.

Calculation: OR = ad/bc

a = exposed + disease
b = exposed + no disease
c = not exposed + disease
d = not exposed + no disease

24
Q

effectiveness vs. efficacy vs. efficiency

A

effectiveness: the ability of the program to produce the intended result in the field
efficacy: ability to produce results under IDEAL conditions
efficiency: ability to produce intended results with a minimum expenditure of time and resources

25
Q

Triad of epi

A

host, agent, and environment

26
Q

when are scatter diagrams best used?

A

used for non-linear relationships and as validity/reliability measure of continuous data

27
Q

descriptive vs. analytical epi

A

descriptive: provides info on the pattern of disease (who, what)
analytical: concerned with identifying or measuring the effects of risk factors, or is concerned with the health effects of specific exposures (how, why)

28
Q

Hawthorne effect

A

when people in a study act differently b/c they know they are being observed

29
Q

double blind vs. single blind study

A

single: patient doesn’t know what tx
double: patient and researcher don’t know

30
Q

Berkson’s bias

A

a form of unrepresentative sample that gives rise to biased estimates of association

31
Q

P value

A

the probability that the effect observed could of resulted from chance alone
ie. <0.05 means there is no more than a 5% chance the observation is due to chance

32
Q

bias

A

the result of a systematic error in the design or conduct of the study that results in a mistaken estimate of an exposure’s effects on the risks of disease
-2 main types: information and selection bias

33
Q

information bias

A

error due to systematic differences in the way data has been gathered from controls and cases

34
Q

selection bias

A

error due to systematic differences between subjects selected for study and those who are excluded

35
Q

recall bias

A

participants inaccurately recall information

36
Q

observer bias

A

researcher records information differently for groups

37
Q

How to reduce bias

A

-matching to decrease selection bias
-randomization
-blinding the study

38
Q

Brainerd’s disease

A

-syndrome of acute onset of severe frequent watery diarrhea
-can occur as outbreaks
-can last for a month or longer
-cause is unknown! even after extensive research

39
Q

infectivity vs. pathogenicity vs. virulence

A

infectivity: the proportion of exposed people who become infected

pathogenicity: the proportion of infected people who become clinically ill

virulence: proportion of infected people who become clinically ill as determined by immunoassay

40
Q

risk values range from:

A

0 to 1

41
Q

attributable risk

A

Proportion of disease incidence or disease risk that can be attributed to a specific exposure

= incidence rate in exposed - incidence rate in unexposed

42
Q

relative risk is to a ___ study as odds ratio is to a ____ study

A

cohort; case control

43
Q

relative risk (aka risk ratio) =

A

incidence rate of exposed / incidence rate of unexposed

= (a/a+b)/(c/c+d)

if relative risk = 1, risk in both groups is equal and you accept null hypothesis that there is no difference. If relative risk > 1, risk of exposed is greater than underexposed. If relative risk <1, risk in exposed is less and it has a protective effect.

44
Q

the problem with continuous variables

A

a cut-off must be established so those who fall below are negative and those who fall above are positive. Cut-off must be chosen to sacrifice either sensitivity or specificity

45
Q

morbidity rate

A

number with disease / number at risk

46
Q

point prevalence

A

the prevalence measured at a particular point in time; the proportion of persons with a particular disease or attribute on a particular date

47
Q

period prevalence

A

prevalence measured over an interval of time

48
Q

numerator of incidence = NEW cases that occurred during a given time period

numerator of prevalence = ALL cases present during a given time period

A

N/A

49
Q

frequently used measures of morbidity

A

-incidence proportion
-secondary attack rate
-incidence rate
-point prevalence
-period prevalence

(see table page 24/79)

50
Q

frequently used measures of mortality

A

-crude death rate
-cause-specific death rate
-proportionate mortality
-death to case ratio (number of deaths assigned to a specific cause during a given time interval)
-neonatal mortality rate
-postneonatal mortality rate
-infant mortality rate
-maternal mortality rate

51
Q

rate ratio

A

compares the incidence rates, person-time rates, or mortality rates of 2 groups. The 2 groups are typically differentiated by demographic factors or by exposure

= rate for group of primary interest/rate for comparison group

rate ratio > 1 when there is increased risk for the group in the numerator

rate ratio < 1 when there is decreased risk for the group in the numerator

when there are equal rates in the 2 groups, the rate ratio will be 1

ACVPM (19 decks)

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