1
Q
prevalence proportion is a measure of
A
disease burden
2
Q
types of prevalence
A
point, period, cumulative lifetime
3
Q
point prevalence is represented by
A
the month
4
Q
period prevalence is represented by
A
the year
5
Q
prevalence proportion
A
total # of cases (new and existing) present in the population during specified time period / total # of person in population during said time period (x 10^n)
6
Q
proportion is
A
part/number considered in comparative relation to a whole
7
Q
ratio =
A
comparison of two or more values with the same units
8
Q
rate =
A
comparison of two or more values with different units
9
Q
cumulative incidence =
A
total # of new cases during a time period / total # of persons AT RISK of developing disease during that time (x10^n)
10
Q
cumulative incidence is also known as
A
incidence proportion
11
Q
incidence density =
A
incident cases / person time
12
Q
person time is calculated by
A
(persons at risk + time at risk)
13
Q
incidence density is expressed as a
A
rate
14
Q
what is the purpose of incidence density?
A
accounts for censored observations to show full picture of incidence
15
Q
relationship b/w incidence and prevalence
A
P / 1 - P
16
Q
P =
A
incidence rate
17
Q
1 - P =
A
duration of disease
18
Q
when disease is relatively rare…
A
1 - P approximately is 1
19
Q
crude mortality rate =
A
total # of deaths from all causes in year Z / # of persons in midyr population of year Z (x100,000)
20
Q
disease-specific mortality is also known as
A
cause-specific mortality
21
Q
disease-specific mortality =
A
of deaths due to specific cause / # of persons in midyear population (x 10^n)
22
Q
age-specific mortality =
A
of deaths in a given age group / # of people in that age group in midyr population (x10^n)
23
Q
infant mortality rate =
A
Number of infant deaths < 1 yr / Number of live births) * 1,000
24
Q
case fatality rate (CFR) =
A
of people dying during specific period of time after diagnosis or onset of disease / # of people with disease (x100)
25
CFR is a rate or proportion?
proportion
26
proportionate mortality =
number of deaths from disease A in community B in year C / total # of deaths in community B in year C
27
age-specific death rates (ASDR) =
number of deaths in age group of interest / estimated midyear population in age group of interest (x10^n)
28
standardized mortality ratio (SMR) =
observed # of deaths per year / expected # of deaths per year
29
odds are
a comparison of probabilities
30
odds =
probability of an event occurring (P) / probability of event not occurring (1 - P)
31
odds ratio is also known as
the cross products ratio
32
null value =
1
33
protective values =>
CIR < 1
IDR < 1
OR < 1
34
risk factors =>
CIR > 1
IDR > 1
OR > 1
35
protective values mean what for risk/rate/odds?
risk/rate/odds for disease is LOWER in the exposed group
36
what do protective values mean for exposure?
exposure REDUCES disease likelihood
37
what do null values mean for exposure and risk/rate/odds of disease?
risk/rate/odds are equal for unexposed and exposed groups
exposure not associated w/ outcome
38
what does risk factors mean for risk/rate/odds?
risk/rate/odds for disease is HIGHER in exposed group
39
what do risk factors mean for exposure?
exposure INCREASES disease likelihood
40
epidemiologic study design typology is based on
design or unit of analysis
41
study design(s) based on design:
observational and experimental
42
observation studies include
cross-sectional
cohort
case-control
43
experimental studies include
clinical trials
field trials
44
study design(s) based on unit of analysis:
individual-level
group or ecologic-level
45
formative application of qualitative research...
provides guidance for creating program materials, tools and culturally appropriate approaches
46
supplemental application of qualitative research...
provides additional info when evaluating a program or study
47
explanatory application of qualitative research...
helps explain unique finidings by providing more context
48
techniques for qualitative research
observational studies
document/text analysis
interview studies
49
interview studies include
in-depth interviews
focus group discussions
(these are most common to epi studies)
50
in-depth interviews method and analysis
method: one on one convos designed to provide a detailed pic of an individual participants
analysis: finding a new and/or recurring theme around health phenomena at interest
51
focus group method and analysis
method: group based interview designed to identify beliefs and opinions of a group of people about a certain topic
analysis: find new and/or recurring theme around health phenomena at interest
52
advantages to in-depth interviews
better method for sensitive topics
can be more private
allows more time to explore ideas with a given person
can yield more detailed and rich information
53
advantages to focus group
allows people to build off each other's comments
new ideas/insights may arise
takes less time than interviewing an individual
opportunity to understand social norms and group dynamics
54
disadvantages to in depth interviews
more resource consuming
more time needed
more cost per person
interviewer must be trained to be as consistent in info obtained across interview but also to probe/continue on certain points brought up
55
disadvantages to focus groups
hard finding time/space for all group members
moderator must be well trained to manage conversation and group interactions
sensitive topics may be more difficult to discuss in group settings
may be difficult to transcribe interview and correctly attribute comments to individuals
56
IDR (incidence density ratio) is also known as...
risk ratio
57
prevalence for comparing disease among exposed vs. unexposed:
a/[a+b] vs. c/[c+d]
58
prevalence ratio for comparing diseased vs. not diseased:
a/[a+c] vs b/[b+d]
59
what was john snow known for?
cholera tracking through water transmission and natural experimentation - 1849
60
endemic disease
of new cases of a disease are identified at or near the usual rate of incidence
61
epidemic aka
outbreak
62
epidemic means that there's
a number of cases identified in clear excess of the previous incidence
63
pandemic means
of new cases is increasing rapidly
and identified across continents and countries
64
model (paradigm) of disease
host, agent, environment
65
host factors from the model of disease
individual characteristics
individual behaviors
66
environment factors from model of disease
physical environment
social environment
67
key characteristics of interest about agent
infectivity
pathogencity
virulence
68
what's a reservoir?
habitat of the agent
69
human reservoirs -->
symptomatic and asymptomatic cases
70
animal reservoirs examples
dogs, bats, cats, mice, mosquitos, etc
71
environmental reservoir examples
water, soil, food, air
72
modes of transmission:
indirect vs. direct
73
direct transmission example
person-to-person contact (sexual, perinatal, skin-to-skin transmission)
74
indirect transmission example
common vehicle (vaccines, drugs, blood)
respiratory
vectorborne (from an insect)
zoonotic (from animals like mosquitos)
fomites (nonliving inanimate objects)
75
fixed population is aka
closed population
e.g. people born in 2005, Vietnam war veterans
76
dynamic population is aka
open population
e.g. population of Cape May
77
population steady state means
when in-migration is equal to out-migration
78
main measures of morbidity
prevalence
incidence
odds
79
cumulative incidence is based on
persons at risk (aka incidence proportion)
80
incidence density is based on
person-time units at risk
81
first level of disease prevention
primary prevention
82
primary prevention is...
the activities that help prevent disease/healthcare problem
83
second level of disease prevention
secondary preventions
84
secondary prevention is
1) IDing and treating asymptomatic persons with sub-clinical disease
OR
2) Early treatment to prevent disease progression
85
odds ratio will over or underestimate (which) ratio
overestimate risk ratio
86
third level of prevention
tertiary
87
tertiary prevention is
Early treatment of disease and prevention of complications
88
measures of association for cross sectional studies
prevalence ratios
prevalence odds ratios
89
when to use PR for cross sectional studies
when prevalence of exposure + outcome are HIGH
90
when to use POR for cross sectional studies
when outcome is RARE
91
strengths of cross sectional studies
easy to conduct
cost-effective
yields basic associations
92
weaknesses of cross sectional studies
Identifying prevalence (P = ID)
Length based bias (cases that are around longer are more likely to be picked up)
can't establish causality
93
types of group level variables in ecologic studies
1) Variables that summarize individual-level data like median household income of a zip code
2) Variables that characterize a “property of the aggregate” like the Minimum driving age by state or # of grocery stores in NYC
94
ecologic fallacy
misinterpretation of group level data as individual level associations
95
ecologic study strengths
Good for exposures with little/no within group variation
Some factors only defined/measured at group level
Does allow estimation of associations (sometimes correlations)
96
ecologic study weaknesses
Main exposure and outcomes data must be available for all groups being studied
Data on ‘other factors’ may be unavailable
Associations, not causation
ECOLOGIC FALLACY
97
purpose of cross sectional study
to describe the prevalence of a characteristic or condition in a population at a single point in time
98
cohort study purpose
when there is a public health imperative to identify health threats/preventive treatments
99
Selecting population groups for cohort studies
Once a population is identified, want study sample to include those people or groups that are susceptible to disease onset
Restriction: Individuals with outcome of interest (prevalent cases) or not at-risk disease are excluded
100
rare exposures for cohort studies
Need special populations: e.g. occupational workers, etc.
Ex: Incidence of lung cancer among coal miners
101
common exposures for cohort studies
Can use a general cohort that will facilitate accurate and complete ascertainment of data (Doctors, nurses, well-defined communities)
Ex: Incidence of CHD among residents of Framingham, MA
102
for cohort studies, at baseline and follow-up visits, what is used
Questionnaires (verify by records)
Medical exams
Physician, hospital, health plan records
Disease registries (e.g. cancer, etc.)
Death certificates
103
measures of association for cohort studies
risk ratio
rate ratio
OR
104
cohort study strengths
Select groups based on exposed/unexposed status
Recall bias minimized
Can study multiple exposures
Minimize bias in ascertainment of exposures and covariates; esp. In prospective studies
Can study multiple outcomes**
Time order established
Efficient for rare exposures
Provides incidence rate of disease
105
cohort study weaknesses
Loss to follow-up
If large number of subjects is required or long follow-up = $$ or logistically challenging; especially for prospective design
Hard to study rare diseases
Changes over time in staff/methods
Little control over nature and quality of data in retrospective designs
106
if SMR = 1 then
observed deaths = expected deaths
107
if SMR > 1 then
observed deaths > expected deaths
108
if SMR < 1 then
observed deaths < expected deaths
109
when to use indirect standardization?
when ASDRs are known for one population and not another
110
risk ratio is also known as
cumulative incidence ratio (CIR)
111
cumulative incidence ratio (CIR) aka
risk ratio
112
risk in exposed =
a/(a+b)
113
risk in unexposed =
c/(c+d)
114
risk ratio =
a/(a+b) / c/(c+d)
115
incidence density ratio (IDR) aka
rate ratio
116
rate in exposed =
a/PY exposed
117
rate in unexposed =
c / PY unexposed
118
rate ratio =
a/PY exposed / c/PY unexposed
119
attributable risk (AR) =
risk in exposed - risk in unexposed
120
attributable risk %
(Risk in exposed - Risk in unexposed) / Risk in exposed * 100
121
PAR (population attributable risk) =
(Risk in total) - (Risk in unexposed)
122
PAR % =
(Risk total - Risk unexposed) / Risk total
123
risk total =
(a+c)/(a+b+c+d)
124
study design for cross-sectional
defined population: gathered data from one pt in time
four possible groups: exposed w/ disease, exposed w/o disease, not exposed w/ disease, not exposed w/o disease
125
ecologic study strengths
effective for exposures within low within-group variation
useful for factors defined or measured at group level
facilitates estimation of associations or correlations
126
ecologic study weaknesses
requires main exposure and outcome data for all groups identified
limited availability for other data factors
only finds associations NOT causation
RISK OF ECOLOGICAL FALLACY
127
crash course of cross sectional studies
exposure and outcome data collected simultaneously
provides prevalence of disease/risk factors at given moment in time
no individual follow ups
128
crash course of ecological studies
units of analysis: groups/aggregates (e.g. countries, regions, neighborhoods)
measurement --> exposure and outcome measured for each group
design flexibility: can employ cohort, case-control, and experimental designs at ecological level
129
prospective cohort studies pros/cons
pros: better exposure data, less bias
cons: expensive time, consuming
130
retrospective cohort studies pros/con
pros: cheaper, faster, effective for diseases w/ long latency
cons: exposure data limited
131
fixed cohort study
established at study onset w/ no new participants added
loss of participants minimized
132
fixed cohort study w/ withdrawals
sample size can/will change, affecting study
133
open/dynamic cohort
adds participants over course of study
134
x
x
135
cohort studies cumulative incidence among exposed, unexposed, total
among exposed: a/(a+b) x 10^n
among unexposed: c/c+d * 10^n
total: a+c/a+b+c+d * 10^n
136
cohort studies' measures of impact
AR, AR %, PAR, PAR%
137
when to use case control studies
obtaining exposure data is hard
long induction / latent period for disease
disease IS RARE
limited knowledge abt disease
dynamic population
138
nested case control study
nested inside a cohort study
uses cohort study data
studies a condition different from the cohort study
139
case-control sample selection for CASES
cases should represent persons w/ disease
population/hospital-based or found from screening data or specialty clinic
140
case-control sample selection for CONTROLS
pick people who could be cases
if picking from hospital, person should not have disease/conditions related to disease
141
matching for controls
group matching: proportion of individuals with disease (i.e. gender) is same for cases/controls
individual: matched w/ similar control
142
measure of association for case-control
exposure odds ratio
143
odds of exposure among cases
a/c
144
odds of exposure among controls
b/d
145
exposure odds ratio =
ac/bd
146
EOR interpretation =
odds of exposure among cases is X times the odds of exposure among controls
147
prevalence ratio exposed =
[a/(a+c)] / [b/(b+d)]
148
Ratio for comparing DISEASE among exposed vs. unexposed =
PRd = [a/(a+b)] / [c/(c+d)]
149
Ratio for comparing EXPOSURE among diseased vs no disease =
PRe = [a/(a+c)] / [b/(b+d)]`
150
population attributable risk (PAR) =
(a+c)/(a+b+c+d) - c/(c+d)
151
par % ratio =
(a+c)/(a+b+c+d) - c/(c+d) / (a+c)/(a+b+c+d) * 100
fall 2025
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