Epidemiologic Risk Measures (wk 5) Flashcards
What is the study of the distribution and determinants of disease, injury or dysfunction in human populations used as a research approach?
Epidemiology
Examples of what epidemiologists do:
- identifying the source of the outbreak
- monitoring and tracking the disease
- studying the disease
- developing guidance for actions to slow the spread and lessen its impact
When are descriptive epidemiologic studies done?
when little is known about the occurrence or determinant of health conditions
Descriptive epidemiologic studies may be presented as what 3 types of studies?
case reports, correlational studies, or survey studies
Descriptive epidemiologic studies are purposed to answer:
- Who experiences this disorder?
- Where is the frequency of disorder highest or lowest?
- When does the disorder occur most or least frequently? (Disease frequency)
- Prevalence
- Incidence
What is a proportion reflecting the number of existing cases of a disorder relative to the total population at a given point or period in time?
(# of existing cases of a disease at a given point in time)/total population at risk
Prevalence
Interpret:
P = 21.8% obesity survey
This is called the point prevalence, what does that mean?
there is a 22% probability that any randomly selected individual from this population would be obese
point prevalence - it reflects the cross-sectional status of the population (certain fixed time point)
Interpret:
p = 40.6% 1 – year period random sample
This is called the period prevalence, what does that mean?
Interpretation – there is a 41% probability that any randomly selected individual from this population would have upper limb musculoskeletal complaints
This value is referred to as period prevalence because it combines the existing cases with new cases during the period of one year
What is a proportion reflecting the number of new cases of a disorder relative to the total population at a given period in time?
(# of new cases during given time period)/(total person - time)
Incidence rate (IR)
WHat does person-time mean?
the time periods of observation for all individuals in the population at risk during the study time frame
IR is often considered a more efficient measure as it allows for inclusion of all subjects while CI (cumulative incidence) only accounts for what?
for those subjects who were available for the entire study period
Interpret:
IR = 3606 new cases/1794565 person-years = .002
CI = 3606 new cases/121700 female nurses = .029
2 cases per 1,000 person years
3 cases per 100 people at risk
Birth rate and mortality rate are examples of what type of measure?
Incidence
Exploratory epidemiologic studies are performed to assess the relationship between what two things?
Exposure and disease status
When an association is found to exist between the exposure and disease status, that specific exposure represents a _____ for the disease
a risk factor
Exploratory epidemiologic studies may be presented as
Case control studies
Cohort studies
The likelihood that someone who has been exposed to a risk factor will develop the disease, as compared with one who has not been exposed -
(incidence of disease among exposed)/(incidence of disease among unexposed subjects)
relative risk (RR)
Measures of RR are appropriate for use with what type of study?
cohort
Using a 2x2 contingency table, how would you calculate RR (equation)?
(a/(a+b))/(c/(c+d))
a: those who have the disease and were exposed
b: those who do not have the disease and were exposed
c: those who have the disease and were not exposed
d: those who do not have the disease and were not exposed
a+b: those who were exposed
c+d: those who were not exposed
a+c: those who have the disease
b+d: those who don’t have the disease
If the RR = 1, what does that mean for the IR of the outcome for the exposed and unexposed?
Exposure presents no excess risk for outcome
What is the equation for cumulative incidence?
a/(a+b)
Interpret:
RR >1
RR = 1
RR<1
- RR > 1.0 indicates an increased risk
- RR = 1.0 indicates no excess risk
- RR < 1.0 indicates a decreased risk of developing the disorder
An estimate of RR when RR is not appropriate to compute -
Odds Ratio (OR)
WHat measure is more appropriate for case-control studies? Why?
Odds Ratio (OR) - A case-control study differs from a cohort study in that subjects are purposefully chosen based on the presence or absence of disease (cases or controls), and therefore we cannot determine the rate of incidence of the disease
Equation for OR using a 2x2 table =
ad/bc
Interpretation of OR value:
OR>1
OR=1
OR
- OR > 1.0 indicates an increased risk
- OR = 1.0 indicates no excess risk
- OR < 1.0 indicates a decreased risk of developing the disorder
What type of research is finding relationships between variables (not cause and effect)?
Exploratory research
What type of research study is this?
- To study the relationship between long-term medical conditions and depression
Exploratory research
T/F Exploratory research explores the relationship between data and can make predictions
False, can not make predictions
Prospective research is?
- variables are measured through direct recording in the present
- the researcher follows subjects as they progress
Retrospective research is?
- data have been collected in the past
2. data often obtained from medical records, databases, or surveys
What is a longitudinal study?
- data are collected in a time sequence with repeated measurements at prescribed intervals
- describe pattern of change
What is a cross-sectional study?
- the researcher studies a stratified group of subjects at one point in time
- the researcher may compare the characteristics of those strata to draw conclusions
What is a cohort study?
- selects a group of subjects who do not yet have the outcome of interest and follows them to see if they develop the disorder
In a cohort study what are you comparing?
- comparing the incidence of specific outcomes in those who were and were not exposed
What is a case-control study?
cases - with disorder
controls - without disorder
- the researcher looks backward in time to determine if the groups differ with respect to their exposure histories
