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These studies compare subjects who have the condition (case) with patients who do not have the condition (controls)
Case control studies
Case control studies are often used for…
studying rare diseases or outcomes and long latency periods (cancer)
The purpose of case control studies are…
to determine whether an exposure is associated with an outcome (disease of condition)
These are advantages of which type of study?
efficient for rare diseases
quick and inexpensive (compared to others)
study multiple exposures or risk factors
requires fewer subjects
Case-controls study
There are challenges for which type of study?
recall bias - participants may not remember past exposures accurately
selection bias - poorly choses controls can skew results
cannot establish causation - only associations
temporal ambiguity - difficult to be certain exposure preceded disease
Case-control study
What type of case control study is:
Each case is paired with one or more controls based on specific characteristics (age, sex)
Matched case control study
Which type of case-control study is:
Conducted within a defined cohort, cases and matched controls are selected from the same cohort
Nested Case control study
Which type of case control study is:
A variation where controls are randomly selected from the cohort, not matched
Case-cohort study
What are best practices for case-control studies?
Clear case definitions
appropriate controls
blind interviewers or standardized data collection tools
matching and statistical adjustment
These studies are observational and longitudinal that follows a group over time to examine the association between exposures and outcomes
Cohort studies
What is the purpose of cohort studies?
to determine whether an exposure is associated with the risk of developing a particular outcome
helps establish relationship between exposure and outcome
This type of cohort study:
starts before any outcomes occur and move forward in time
participants are followed to observe outcomes
Prospective cohort study
This type of cohort study:
both exposure and outcome have already occurred at the start of the study
investigators look back in time in records or databases to classify exposure and outcomes
Retrospective cohort study
Using medical records from the past 20 years to compare disease rates in people exposed vs unexposed to a chemical. Is an example of what type of study?
Retrospective cohort study
Following smokers and nonsmokers for 10 years to see who develops lung cancer. Is an example of what type of study?
Prospective Cohort Study
What is the odds ratio?
What do the following represent?
>1
< 1
= 1
odds ratio estimates the association between exposure and outcome
> 1: exposure might be a risk factor
< 1: exposure might be protective
= 1: no association
What is the relative risk ratio/incidence rate ratio?
What do the following represent?
>1
<1
=1
compares the risk of developing the outcome in exposed vs unexposed individuals
>1: may increase risk
<1: may be protective
=1: no association
There are advantages of what type of study?
establish temporal relationships
incidence and relative risk calculations
study multiple outcomes from a single exposure
less recall bias
Cohort study design
These are challenges of which study design?
time consuming
expensive
loss to follow-up (attrition bias)
not efficient for rare diseases
may involve confounding variables if not properly controlled
Cohort study design
What type of cohort study is a fixed group, no new participants added
closed cohort study
What type of cohort study has participants that can enter or leave over time
open cohort studies
what type of cohort study is a case controlled study conducted within a cohort, an efficient way to analyze expensive or rare exposures
nested case control study
What are best practices for cohort studies?
well-defined inclusion/exclusion criteria
accurate exposure measurment at baseline
minimize attrition bias
control confounding variables - via stratification, regression, or matching
ensure sufficient follow-up time to capture outcomes
What are some major differences between cohort and case-control studies?
Time direction, outcome status at start, best for, measures, cost/time, temporality
Time
Cohort - prospective or retrospective
Case-control - retrospective
Outcome
cohort - outcome free
case control - cases already have outcome
Best for
cohort - rare exposures, common outcomes
case control - rare outcomes, long latency
Cost
cohort - higher
case control - lower
Temporality
cohort - strong
case control - weak
these aim to summarize the best available evidence
Systematic review
true or false.
all meta-analyses should be based on systematic reviews, but not all systematic reviews include a meta analysis
true
this is a quantitative technique that combines the statistical results of multiple studies. ex. an overall risk ration, odds ratio, or mean difference
Meta-analysis
what is the fixed effect model?
assumes one true effect size, used when studies are very similar
what is a random effects model
assumes effect sizes vary across studies, accounts for heterogeneity
These are advantages of what?
reduces bias through transparent methodology
provides a comprehensive summary of evidence
systematic review
There are advantages of what?
increases statistical power
provides precise estimates of effect
can identify subtle effects missed in individual studies
Meta-analysis
What is the equation for prevalence
number of existing cases / total population at time
What is the equation for incidence
#new cases / (total population - those with the disease)
What is the EER equation?
Number of events in experimental group / total number in experimental group
What is the equation for CER?
number of events in control group / total number in control group
What is the equation for absolute risk reduction?
CER - EER
What is the equation for relative risk?
EER/CER
What is the equation for Relative risk reduction?
(CER - EER) / CER
What is the number needed to treat equation?
1/(CER-EER)