02: Study Design Flashcards
(59 cards)
1
Q
What is the importance of study design?
A
- data cannot directly answer questions of interest
- study design determines which data are collected/examined
- data require transformation via analysis and interpretation
- research questions we can ask depend crucially on the study design
2
Q
What are the 3 overarching study design ‘families’?
A
- experimental studies
- observational studies
- meta-analysis studies
3
Q
What are the 6 specific study designs?
A
- meta-analysis
- trials
- cohort
- case-control
- cross-sectional
- case report/case series
4
Q
What is the unit of analysis?
A
5
Q
What are the 2 types of meta-analyses?
A
- meta-analyses of experimental studies
- meta-analyses of observational studies
6
Q
What do observational and experimental studies have in common?
A
can both make causal claims
7
Q
What are observational studies?
A
interventions or exposures are not assigned or manipulated, just observed
- researchers observe what happens under different interventions/exposures
8
Q
What are experimental studies?
A
interventions or exposures are assigned or manipulated
- generally considered higher quality evidence – less bias, higher confidence in causality claims
9
Q
If there are ethical concerns, what study type is the only possible study type?
A
observational
- any exposure with evidence of harm
- smoking, asbestos, air pollution
- infectious disease status
10
Q
If the exposure cannot be changed, what study type is the only possible study type?
A
observational
- race/ethnicity
- presence/absence of a genetic trait
- chronic disease state
11
Q
What do all trials have in common?
A
interventions or exposures are assigned or manipulated by researchers
12
Q
What are non-randomized trials?
A
treatment is assigned, but not at random
13
Q
What are randomized trials?
A
treatment is assigned at random (most common)
- individuals meeting eligibility invited to enroll, randomized to a treatment or intervention, followed over time for outcome/endpoint occurrence
- expensive, time-consuming, not always possible
14
Q
What is the idealized health research study design (gold standard)?
A
randomized trials
15
Q
What do randomized trials require?
A
- pre-specified protocol – eligibility criteria, recruitment plan, randomization method, treatment/intervention and outcome or endpoint definitions, statistical analysis plan
- ‘equipoise’ – no evidence of harm or benefit for intervention
- blinding
16
Q
What is blinding?
A
trial participants, treating providers, and statistical analysts do not know which patient received which treatment
17
Q
What is a placebo controlled trial?
A
randomized trial where one group receives a treatment, while the other receives a placebo that looks like the treatment
18
Q
What are the expected outcomes of randomized trials?
A
patients assigned to treatment A are expected to be comparable (exchangeable) with patients assigned to treatment B
- still susceptible to bias and flawed study design and implementation
19
Q
What are observational studies with no controls?
A
- simply report outcomes of a single group
- ‘hypothesis-generating,’ anecdotal
- lowest quality evidence, cannot establish cause and effect between an exposure and outcome
- can draw attention to an important clinical question/concern
20
Q
What are the types of observational studies with no controls?
A
- case series
- case report
21
Q
What are case series?
A
> 1 individuals with common clinical feature
22
Q
What are case reports
A
1 individual
23
Q
What are the 2 types of observational studies with controls?
A
- followed over time
- no follow-up over time
24
Q
What are the 2 types of observational studies with controls that are followed over time?
A
- cohort studies
- case-control studies
25
What are cohort studies?
select individuals from the source population into sample based on meeting cohort inclusion criteria (ie. not based on outcome status)
- followed over time for outcome status
26
What is assessed in cohort studies?
exposure status is assessed
- exposure status is not assigned/manipulated, but is based on real-world treatment
- to compare outcome frequency among exposed and unexposed, these groups must be exchangeable (comparable)
27
What are the advantages of cohort studies?
- does establish temporal sequence of events for causal inference
- can establish rates (events per person-time), incidence
- can evaluate multiple outcomes
28
What are the disadvantages of cohort studies?
- potential bias arising from differences between exposed and unexposed individuals (confounding)
- often requires a large sample, takes a long time to observe outcomes
- costly
- less efficient for rare outcome
29
What are case-control studies?
select individuals into sample based on outcome status
- outcome status is ‘starting point’ – determines selection into the sample
- look back in time for exposure frequency
30
What are cases in case-control studies?
individuals with the outcome of interest
31
What are controls in case-control studies?
individuals without the outcome of interest, comparable to cases
32
Is selecting cases in case-control studies hard?
no – usually straightforward
33
Is selecting controls in case-control studies hard?
yes
- selected from the same source population that gave rise to cases
- controls must be comparable to cases, similar with respect to potentially confounding factors
- selected independently of their exposure status – often selected via matching
34
What are the advantages of case-control studies?
- efficient for rare outcomes, outcomes that take a long time to develop
35
What are the disadvantages of case-control studies?
- potential bias arising from differences between exposed and unexposed individuals (confounding), control selection (difficult to select similar/comparable controls), exposure assessment occurring after the outcome (information bias)
- cannot examine multiple outcomes, cannot examine outcome rates or absolute risk/incidence
36
What is matching in case-control studies?
selection of controls to match specific characteristics of the cases
- can be 1:1 (cases:controls) or other ratio
37
What are the 2 types of matching in case-control studies?
- individual matching
- frequency matching
38
What is individual matching in case-control studies?
select a specific control per cases by matching variable (ie. date of birth)
39
What is frequency matching in case-control studies?
select controls to get the same distribution of variables as cases
40
What type of observational study with controls are not followed over time?
cross-sectional studies
41
What are cross-sectional studies?
exposure/intervention and outcomes are measured at the same time – ‘snap-shot’ view
42
What are the advantages of cross-sectional studies?
- simple to carry out, inexpensive
- can evaluate multiple outcomes
- can measure outcome prevalence (% with outcome at single time point)
43
What are the disadvantages of cross-sectional studies?
- does not establish the temporal sequence of events for causal inference
- cannot establish rates (events per person time) or incidence (proportion of population that develop an outcome)
44
Comparison of Time in Observational Studies
- cross-sectional study: present
- case-control study: present to past
- cohort study: present to future
45
What is the outdated use of retrospective vs. prospective?
- prospective: cohort and randomized trials
- retrospective: case-control
46
What is the key distinguishing factor of retrospective vs. prospective?
- prospective: exposure measurement cannot be influenced by the outcome
- retrospective: exposure measurement can be influenced by the outcome
47
What is the updated (better) definition of retrospective vs. prospective?
- prospective: exposure measured/collected prior to the outcome
- retrospective: exposure measured/collected at the same time/after as the outcome
48
Why do we care about different study designs?
- level of evidence depends on study design
- each study design is susceptible to different biases
49
List the evidence hierarchy based on quality of evidence, from highest to lowest.
increasing study quality, decreasing bias
- meta-analysis
- experimental studies
- cohort studies
- case-control studies
- cross-sectional studies
- case reports and case series
- expert opinion
50
What is the proposed new evidence-based medicine pyramid?
51
What is study registration?
involves submitting a study protocol to an online, public access, searchable registry
52
What type of studies is study registration available for?
both experimental and observational studies
53
What does study registration do?
- promotes transparency – prevents selective reporting, reduces publication bias
- prevents duplication – inefficient use of limited resources, patient time
- increases awareness for patients, healthcare providers
- condition for publication – in some cases required by law (ie. ClinicalTrials.gov)
54
What is a study protocol?
- complete description of PICO/PECO components
- complete description of the statistical analysis plan
55
What is a reporting guideline?
a simple, structured tool for health researchers to use while writing manuscripts
56
What do reporting guidelines do?
provides a minimum list of information needed to ensure a manuscript can be:
- understood by a reader
- replicated by a researcher
- used by a healthcare provider to make a clinical decision
- included in a systematic review
57
What are the reporting guidelines for randomized trials?
Consolidated Standards of Reporting Trials (CONSORT)
58
What are the reporting guidelines for the 3 types of observational studies?
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE)
59
What are the reporting guidelines for meta-analyses?
Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA)
