Lecture 3 - Analytical Study Design (Part 1) Flashcards by James Ozorkiewicz

attempt to provide insight into etiology or find/ determine better patient outcomes

explanatory studies

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has an active intervention from the investigator

experimental explanatory study

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investigator observes nature

observational explanatory study

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examples of experimental explanatory studies

controlled trial
clinical trial
educational intervention
healthcare trial
intervention trial

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ex’s of observational explanatory studies

case-control
follow up
cross -sectional
cohort (fancy way of saying follow-up)

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observational studies

case-control
follow up
cross -sectional
cohort (fancy way of saying follow-up)

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snapshot in time that doesn’t show causality

cross-sectional study

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examines the relationship outcomes and other variables of interest as they exist in a defined population at one particular time

cross-sectional study

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determines prevalence (% of population) not incidence (rate)

cross-sectional study

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prevalence

(% of population)

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not incidence

rate

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can a cross-sectional study show causality?

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Do cross-sectional studies separate cause/ effect?

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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

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another name for cross sectional study?

prevalence studies

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gives the disease burden right now

prevalence study (cross sectional study)

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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

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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

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What are observational studies?

case-control studies

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retrospective study that looks back at causes

case-control study

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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

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the researcher LOOKS BACK to identify factors or exposures that might be associated with the illness

Case-control study

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this type of study design may follow a case-series (as a retrospective look at causes)

case-control study

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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

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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 ```