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EPI > EPI Final Exam > Flashcards

EPI Final Exam Flashcards

1
Q

How to Calculate Prevalence Period

A

existing cases at start + new cases over a period of time/ size of population at start of time period = %

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2
Q

How to calculate prevalence point

A

existing cases at “point” in time/ size of population at “point” in time = %

a single point in time

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3
Q

how to calculate incidence proportion (cumulative incidence= CI)

A

number of people developing the outcome/ number of people at risk

CI=IR x time

estimation for risk in a population “at risk” (candidate population)- fixed population

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4
Q

how to calculate incidence rate (IR)

A

number of people developing the outcome/ total time at risk

estimates change in risk over time in a population at risk- fixed or dynamic population (instantaneous risk)

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5
Q

how to calculate incidence density

A

number of new cases / sum of the person-time of the at-risk population

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6
Q

how to calculate person time incidence

A

the number of new cases/ person time at risk through observation

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7
Q

how to calculate crude death rate

A

number of death in a given period/ the population exposed to risk of death in that period

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8
Q

how to calculate proportionate mortality

A

number of deaths from a given cause in a specific period of time/ total number of deaths in the same period

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9
Q

how to calculate case fatality rate

A

proportion of individuals with a disease who die from the disease

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10
Q

what is age adjustment

A

standardization

  • provides a valid comparison using a single number for each population
  • transform a measure based on a specific factor composition of a reference population
  • referred to as the direct method of standardization
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11
Q

why is age adjustment used

A

almost all diseases occur at different rates in different age groups, so for accurate analysis- its going to be important to take this into account

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12
Q

what are age specific rates

A

total number of health events for the specific age group of interest/ total population in that age group

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13
Q

how are age specific rates used

A

multiplying the age-specific rates of disease by age- specific weights

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14
Q

what is the formula for risk difference/excess risk

A

Re-Ru/Ru = RR -1 (expressed as percent

the null value is 0%
not a proportion just a ratio

“relative risk”- often described as the percent change relative to the reference risk

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15
Q

what is the formula for risk ratio

A

RR = Re/ Ru
Risk ratio & rate Ratio
Rate Ratio : Rr = IRe/ IRu

Prevalence ration = Pe/Pu

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16
Q

what is the formula for odds ratio

A

(a/b)/ (c/d) or ad/bc

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17
Q

what is the formula for relative risk

A

deaths or disease risk in a specific population/ risk of people from all other groups

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18
Q

how do you calculate and interpret risk difference/excess risk

A

RE-Ru/Ru = RR -1 (expressed as a percent)

  • increase linearly above one and exponentially below one

RR= Rm/Rf and RR = Rf/Rm

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19
Q

how do you calculate and interpret risk ratio

A 
no effect (null value) is 1.0 
RR >1 indicates GREATER risk for exposed population relative to reference population

RR < 1 indicates lesser risk for exposed population relative to reference population

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20
Q

how do you calculate and interpret odds ratio

A

odds of the first group/ odds in the seconds grouphow

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21
Q

how do you calculate and interpret relative risk

A

death or disease risk in a specific population/ risk of people from all other groups

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22
Q

definition of attributable risk

A

amount of proportion of incidence of disease or death in individuals exposed to a specific risk factor

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23
Q

definition of population attributable risk

A

risk in the total population that would not have occurred if exposure had not occurred )may also be expressed as number of cases)

PRD = R total - Ru

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24
Q

what type of epi study uses case control sutdies

A

main features:

  • individuals with the outcome are identified (cases)
  • individuals without the outcome are identified (controls or referents)
  • exposure is determined for cases and controls at an appropriate time IN THE PAST (there is no follow-up)
  • the association between exposure and health outcome is quantified using the odds ratio
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25
Q

what type of epi study uses cohort studies

A

population with one or more common characteristics or experiences

experimental (intervention) studies

Observational Cohort Studies

  • prospective cohort
  • retrospective cohort
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26
Q

what type of epi study uses ecological studies

A

data representing entire populations are used to evaluate an association

exposure status and outcome status are single values applied to the entire population

correlations can be positive, negative, or zero

may not represent the association that exists on the individual level (ecological fallacy)

more complicated relationships can be masked

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27
Q

what type of epi study uses cross sectional studies

A

Assess prevalence of population in characteristics at a “point in time” this means information on current status is collected from a participant only once (no follow up)

information on individuals associations but lacks temporal relationship between :exposure” and outcome

measure of association is the odds ratio (not an estimate of RR for cross-sectional studies)

classified by whether the data is provided by participants for come from an evaluation - interview or examination

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28
Q

conditions to use a case control study

A

exposure data are difficult or expensive to obtain

small number of participants

disease is rare

disease has long induction and latent period

little is known about the disease

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29
Q

conditions to use a cohort study

A

good evidence is needed for risk factor

exposure is rare

desire accurate measurement of exposure

little is known about the exposure

limitations: expensive, long time commitment

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30
Q

conditions to use an ecological study

A

One of the least valid
data representing entire populations are used to evaluate an association

exposure status and outcome status are single values applied to the entire population

correlations can be positive, negative, or zero

may not represent the association that exists on the individual level (ecological fallacy)

more complicated relationships can be masked

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31
Q

conditions to use a cross sectional study

A

Almost the least valid

strengths: inexpensive and quick , generalizability , useful for public health planning
limitations: prevalence is the measure of disease frequency, not time separation between exposure and outcome, data are prone to bias and often self reported

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32
Q

death rate

A

number of people dying from a condition in a specified population/ number of people in the specified population = deaths per 100,00

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33
Q

What is external validity

A

the relevance of internally valid study results to populations with characteristics different from the source population, also called generalizability

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34
Q

What is internal validity

A

the extent to which studies result represent the true association between a factor of interest and the health-related outcome for the source population

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35
Q

What is the major differences between internal and external validity

A

When the goal of the study is to evaluate a potential association between a factor and health related outcome, there are two types of validity

when the goal of the study is to estimate a characteristic of a source population, then there is onyl one validity

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36
Q

What is systematic error

A

always results in bias

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37
Q

what is random error

A

may result from bias for an individual measurement but not necessarily an average measurement

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38
Q

what is included under systematic error

A

misclassification, information, selection

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39
Q

what is confouding

A

mixing of effects between a factor of interest, a health outcome, and a third factor that is a risk factor for the health outcome of interest, but is not of interest in the study. This third factor is often referred to as a confounder

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40
Q

what are the 3 criteria for confounding

A
  1. variable must be a risk factor for the outcome in BOTH the exposed and unexposed populations
  2. the potential confounder must be associated with the exposure in the population that produced the cases
  3. the confounder can not be an intermediate step in the causal pathway between the factor of interest and the health outcome
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41
Q

what is selection bias

A

bias that occurs at the selection of participants

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42
Q

what is information bias

A

incorrect portrayal or records of information or calculation

43
Q

what is misclassification bias

A

individual is assigned to a different category than they should be

44
Q

What are the strategies to control confounding

A 
randomization 
restriction 
matching 
stratification 
adjustment 
multivariate analysis
45
Q

What is used to reduce bias

A

placebo- pharmacologically inactive substance given as a substitute for an active substance

sham procedure-bogus procedure designed to resemble a legitimate procedure

blinding- withholding idtentiy of group assignment

46
Q

what is confounding ( direction away, towards the null)

A

occurs when risk factors for the outcome, other than that being studied distorts the measures association between the factor being studied and the outcome

47
Q

What is matching

A

selection of unexposed subjects that have characteristics identical to cases

48
Q

What sets the data towards the null (ex)

A

ex. CRUDE RR = 1.5
Adjusted RR = 2.5

CRUDE less than

negative confounding-bias towards the null

49
Q

What sets the data away from the null (ex)

A

ex. CRUDE RR= 3
Adjusted RR = 2

CRUDE larger

positive confounding- bias away from the null

50
Q

Define sensitivity

A

proportion of people with the disease who have also a positive result for the test, sign, or symptom.

this is a measure of the ability of a screening test to correctly identify people WITH the outcome of interest

51
Q

Define specificity

A

the proportion of people among those who do not have the disease who also have a negative result for the test, sign, or symptom.

This is a measure of the ability of a screening test to correctly identify people WITHOUT the outcome of interest

52
Q

Define negative predictive value

A

proportion of people with a negative test results who actually do not have the outcome of interest- measures accuracy of negative test results

53
Q

define positive predictive value

A

proportion of people with a positive test result who actually have the outcome of interest- measure of the accuracy of a positive test result

54
Q

what is a p-value

A

the probability the point estimate based on data would be as far from the null hypothesis or farther than that actually obtained - probability of a false positive conclusion

55
Q

how do you interpret a p-value

A

p value LESS than a predetermined cutoof is taken to indicated as “statistically significant” result

most typical cutoff is p = .05

Null hypothesis is true, do not reject - correct
Null is true, rejct - type 1 error (fals pos)
Null false, do not reject - type 2 error (false neg)
Null false, reject- correct

56
Q

what is an epidemic

A

increase in disease frequency of a disease above what is normally expected in a given population and area

57
Q

what is an endemic

A

constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. Hyperendemic refers to persistent high levels of disease occurrence

58
Q

what is a pandemic

A

an international epidemic

59
Q

what is the difference in epidemic, endemic, and pandemic

A

epi is in a given area
pan is worldwid
end is a geographic area

60
Q

Who is included in “externally valid”

A

entire Us population, reference target popualtion, source population

61
Q

Null hypothesis: Ho

A

assumed value or preconceived notion for a population parameter (usually the null value for the RR or OR is =1)

62
Q

what is infectivity

A

capacity of an agent to enter and multiply in a susceptible host

63
Q

what is virulence

A

capacity of an agent to produce a sever outcome course the most severe outcome would be death

64
Q

what is antigenicity

A

capacity of an agent to induce antibody production in a host

65
Q

what is pathogenicity

A

capacity of an agent to cause disease in the infected host

66
Q

what are the types of transmission

A

direct or indirect

67
Q

what is reproductive number

A

r= 1 correspond to constant disease
r> 1 corresponds to increased disease
r<1 corresponds to reduced disease

empirical measure that allows comparison of epidemic potential for different infectious disease under different conditions

68
Q

what is vector born transmission

A

indirect infectious agent is conveyed to a susceptible host by some form of living organism called a vector

69
Q

Alternative Hypothesis Ha

A

the opposite or complement of the null hypothesis- usually not one but could be greater or less than

70
Q

Direct transmission

A

immediate transfer of an infectious agent from an infected host or reservoir to a susceptible host

airborne, direct contact, bites

71
Q

indirect transmission

A

vehicle borne, vector born

72
Q

indirect transmission

A

vehicle borne, vector born

73
Q

Type of carriers

A

inapparent
incubating
convalescent
chronic

74
Q

inapparent carrier

A

individual that is infectious in the absence of symptoms throughout the course of their infection

75
Q

incubating carrier

A

an individual that is infectious during the incubation period

76
Q

convalescent carrier

A

an individual that has recovered from disease but remains infectious

77
Q

chronic carrier

A

an individual continues to harbor the viable organism indefinitely and remains infectious to others

78
Q

chronic carrier

A

an individual continues to harbor the viable organism indefinitely and remains infectious to others

79
Q

Active Immunity

A

attained naturally by infection or immunization

80
Q

passive immunity

A

attained naturally but WITHOUT infection

81
Q

validity =

A

accuracy

82
Q

reliability=

A

precision

83
Q

reliability=

A

precision

84
Q

true or false: the purpose of screening is to identify symptomatic cases of disease

A

false

85
Q

true or false: screening is conducted in order to reduce morbidity and improve survival

A

true

86
Q

true or false: the positive predictive value is more influence by the specificity than the sensitivity of the screening test

A

true

87
Q

true or false: the positive predictive value is more influence by the specificity than the sensitivity of the screening test

A

true

88
Q

In the definition of epidemiology, the phrase “determinants of disease frequency in human population” refers to which of the following

A

WHY it is occuring

89
Q

A study of retirees from a large manufacturing facility found that the average age death among the retirees was greater than the average age death for the general population. What is the best interpretation of this finding

A

the comparison is not valid because the general population contains many individuals that die young

90
Q

Who created the life table

A

John Graunt

91
Q

John Snow’s investigation of cholera epidemic in the mid 19th century was an example of which advance in the history of epi?

A

disease etiology can be investigated in natural experiments

92
Q

Who observed that during the 1918 influenza pandemic, young adults were at greater risk of dying from influenza if they became infected than were middle age adults

A

wade hampton frost

93
Q

What is one reason why randomized clinical trails were developed in the mid 20th century

A

to improve the assessment of efficacy and safety of drug vaccines

94
Q

What is one reason why randomized clinical trails were developed in the mid 20th century

A

to improve the assessment of efficacy and safety of drug vaccines

95
Q

When a single agent can cause multiple different adverse health outcomes and a particular adverse health outcome can be the result of several distinctly different factors, this is referred to as lack of ____

A

specificity

96
Q

Why is it difficult to accurately estimate the average induction and average latent period

A

the start of disease can’t be determined

97
Q

in the causal model for the natural history of disease during the___ period the disease process has already started

A

latent

98
Q

in the causal model for the natural history of disease, the time from the first action of component cause to development of disease is call the ____ period

A

induction

99
Q

a _____ cause is all that is needed for disease to occur

A

sufficient

100
Q

a _____ cause must always be present, but may require additional factors to cause the outcome

A

necessary

101
Q

Which of hill guidelines for causality comes closest to being a requirement for causality

A

temporality

102
Q

several different epi studies on diabetes as a risk factor for dementia found similar results. This support which causality guidline

A

consistency

103
Q

Hill guidelines for causality _____ would be satisfied is the effect of exposure increased as the exposure level increased

A

biological gradient

104
Q

the relationship between the flu virus and the flu could be used as an example of which of the guidelines for causality

A

specificity

EPI (1 decks)

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