Lecture 3 - Analytical Study Design (Part 1) Flashcards
attempt to provide insight into etiology or find/ determine better patient outcomes
explanatory studies
has an active intervention from the investigator
experimental explanatory study
investigator observes nature
observational explanatory study
examples of experimental explanatory studies
controlled trial clinical trial educational intervention healthcare trial intervention trial
ex’s of observational explanatory studies
case-control
follow up
cross -sectional
cohort (fancy way of saying follow-up)
observational studies
case-control
follow up
cross -sectional
cohort (fancy way of saying follow-up)
snapshot in time that doesn’t show causality
cross-sectional study
examines the relationship outcomes and other variables of interest as they exist in a defined population at one particular time
cross-sectional study
determines prevalence (% of population) not incidence (rate)
cross-sectional study
prevalence
(% of population)
not incidence
rate
can a cross-sectional study show causality?
No
Do cross-sectional studies separate cause/ effect?
No
T or F:
The cross sectional study establishes a temporal relationship between risk factors and disease
FALSE:
They do not because they are measured at the same time
another name for cross sectional study?
prevalence studies
gives the disease burden right now
prevalence study (cross sectional study)
What are the strengths of cross-sectional studies?
can assess MULTIPLE outcomes and exposures simultaneously
can be completed QUICKLY
data generated can LEAD TO FURTHER STUDIES
can generate PREVALENCE
What are the limitations of cross-sectional studies?
No time reference “snap shot in time” - like looking at a photograph
only useful for COMMON CONDITIONS
cannot calculate incidence, it is a PREVALENCE study
Results are dependent on the study population
What are observational studies?
case-control studies
retrospective study that looks back at causes
case-control study
study in which patients who already have a specific condition (cases) are compared with people who do no have the condition (controls)
case-control study
the researcher LOOKS BACK to identify factors or exposures that might be associated with the illness
Case-control study
this type of study design may follow a case-series (as a retrospective look at causes)
case-control study
tries to capture the cause and effect relationship by comparing frequency of a risk factor among those who are exposed and not-exposed
case-control study
case think
specific condition
control think
no condition
strengths of case-control studies
good for studying RARE OUTCOMES
can evaluate many exposures
ideal for initial, explanatory idea
Simple & fast - we already know the outcomes (efficient due to no waiting for account to occur)
INEXPENSIVE
T or F: case control studies are very expensive
FALSE
limitations of case-control studies
single outcome
high risk for BIAS
high risk for CONFOUNDING VARIABLES
other factors may exist that influence outcomes
no prevalence nor incidence
can’t make casual interpretations
can’t determine incidence
can’t calculate Relative risk
Potential Biases in Case-Control Studies
Selection Bias
Information Bias
Researcher Bias
Voluntary Responses Bias
Selection bias
an inappropriate selection of cases or controls
What are the strengths of cross-sectional studies?
Selection bias
Information Bias
recall bias (Subject Bias) is the main form of information bias in case-control studies. Occurs when there is a DIFFERENTIAL RECALL of exposure between cases and controls
Researcher Bias
occurs when the researcher / observer evaluates cases vs controls differentially
Voluntary Responses Bias
arises when case subjects who think they have been exposed to responds at a higher rate of controls
can be selected from a variety of sources like hospitals, clinics, registries etc. IF selected from single source, risk factors from that facility may not be generalizable to all patients with that disease
Cases with selection bias due to inappropriate selection
ideally, you want controls to come from the same reference population that cases are derived from. An inappropriate control group can have the opposite effect and obscure an important link between the disease and its cause
Controls with selection bias due to inappropriate selection
to ensure you don’t have selection bias due to controls…. how do we choose our control group?
from the same reference population that cases are derived from
what is selective recall, reporting, or recall bias?
when subjects hold beliefs about the cause of their disease
what is the process of selection the controls so they are similar to the cases in certain characteristics, such as age, race, sex, socioeconomic status, and occupation
matching
for each case selected for the study, a control is selected who is similar to the case in terms of the specific variable
individual
select controls with a certain characteristic that is identical to the proportion of cases with the same characterstic
group-based
what are the problems with matching?
1) if you select too many matching characteristics it is difficulty to find an appropriate control
2) you lose the ability to study a matched variable
employing multiple control groups can do what?
offers independent estimates of exposure among different samples of non-cases. Increases strength of the study
a variant of a case-control study
case-crossover
each case becomes their own individual control
case-crossover
used for transient exposures during a discrete occurence
case-crossover
a cast control study within a large cohort
nested case-control
typically seen with large enrollment studies
controls are samples of individuals who are at risk for the disease / outcome at the time each case of the disease develops
nested case-control
same as nested case-control design, expect controls are randomly chosen from the cohort with which the study began
case-cohort
a group of people who share a common characteristic or experience and all remain in the group for a period of time
cohort
an epidemiologic investigation that follows groups with common characteristics,
cohort study
which is the strongest observational study
cohort study
which cohort study looks forward over time?
prospective
which cohort study goes back in time?
retrospective
identify a group of patients who are already taking a particular treatment or have an exposure, follow them forward over time, and then compare their outcomes with a similar group that has not been affected by the treatment or exposure being studies
prospective
start with a cohort and go back in time to evaluate past exposure to risk factors
retrospective
what are types of potential biases in cohort studies?
selection bias or “lost to follow up” where people with disease are selectively lost to follow-up, and those lost to follow-up differ from those not lost to follow-up
information bias
quality and info different for exposed & non-exposed
OBSERVER BIAS - when observer decides the disease has developed in each subject also knows whether that subject was exposed
What are the strengths of cohort studies?
may study multiple effects of a single exposure
can identify a TEMPORAL RELATIONSHIP between the exposure and disease (outcome)
help CONFIRM CAUSE AND EFFECT of disease and the MAGNITUDE of the effect
can measure INCIDENCE (rate) of disease
can calculate RELATIVE RISK
HIGHEST VALIDITY OF OBSERVATIONAL STUDY DESIGN
what is the highest validity of the observational study design?
cohort studies
what are limitations to cohort studies?
Expensive and time consuming
INEFFECIENT for studying rare diseases
LOSE PARTCIPANTS to follow-up
Risk of CONFOUNDING VARIABLES
Retrospective studies require PRESENCE OF RECORDS or recall
T or F: cohort studies are cheap
False! they are expensive and time consuming
starts with exposure and looks for disease
cohort studies
study that can be prospective or retrospective
cohort studies
common diseases; high risk for drop out; Expensive
cohort studies
start with disease, look for exposure
case-control studies
retrospective always
case-control studies
rare disease; has recall and selection bias; inexpensive
case-control studies
is bias always there?
yes
a good research study will acknowledge bias and also take steps to address bias or reduce it… when is this done?
Study Design Phase or
Analysis Phase
top to bottom what is the “pyramid” for quality of evidence
Meta-Analyses Systematic Reviews Critically Appraised Literature or Evidence-Based Practice Guidelines Randomized Controlled Trials Non-Randomized Controlled Trials Cohort Studies Case Series or Studies Individual Case Reports Background Information, Expert Opinion, Non-EBM Guidelines
