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PHRM 131 > 02: Study Design > Flashcards

02: Study Design Flashcards

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
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2
Q

What are the 3 overarching study design ‘families’?

A
  • experimental studies
  • observational studies
  • meta-analysis studies
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3
Q

What are the 6 specific study designs?

A
  • meta-analysis
  • trials
  • cohort
  • case-control
  • cross-sectional
  • case report/case series
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4
Q

What is the unit of analysis?

A
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5
Q

What are the 2 types of meta-analyses?

A
  • meta-analyses of experimental studies
  • meta-analyses of observational studies
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6
Q

What do observational and experimental studies have in common?

A

can both make causal claims

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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
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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
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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
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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
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11
Q

What do all trials have in common?

A

interventions or exposures are assigned or manipulated by researchers

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12
Q

What are non-randomized trials?

A

treatment is assigned, but not at random

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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
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14
Q

What is the idealized health research study design (gold standard)?

A

randomized trials

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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
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16
Q

What is blinding?

A

trial participants, treating providers, and statistical analysts do not know which patient received which treatment

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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

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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
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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
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20
Q

What are the types of observational studies with no controls?

A
  • case series
  • case report
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21
Q

What are case series?

A

> 1 individuals with common clinical feature

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22
Q

What are case reports

A

1 individual

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23
Q

What are the 2 types of observational studies with controls?

A
  • followed over time
  • no follow-up over time
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24
Q

What are the 2 types of observational studies with controls that are followed over time?

A
  • cohort studies
  • case-control studies
25
Q

What are cohort studies?

A

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
Q

What is assessed in cohort studies?

A

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
Q

What are the advantages of cohort studies?

A
  • does establish temporal sequence of events for causal inference
  • can establish rates (events per person-time), incidence
  • can evaluate multiple outcomes
28
Q

What are the disadvantages of cohort studies?

A
  • 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
Q

What are case-control studies?

A

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
Q

What are cases in case-control studies?

A

individuals with the outcome of interest

31
Q

What are controls in case-control studies?

A

individuals without the outcome of interest, comparable to cases

32
Q

Is selecting cases in case-control studies hard?

A

no – usually straightforward

33
Q

Is selecting controls in case-control studies hard?

A

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
Q

What are the advantages of case-control studies?

A
  • efficient for rare outcomes, outcomes that take a long time to develop
35
Q

What are the disadvantages of case-control studies?

A
  • 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
Q

What is matching in case-control studies?

A

selection of controls to match specific characteristics of the cases

  • can be 1:1 (cases:controls) or other ratio
37
Q

What are the 2 types of matching in case-control studies?

A
  • individual matching
  • frequency matching
38
Q

What is individual matching in case-control studies?

A

select a specific control per cases by matching variable (ie. date of birth)

39
Q

What is frequency matching in case-control studies?

A

select controls to get the same distribution of variables as cases

40
Q

What type of observational study with controls are not followed over time?

A

cross-sectional studies

41
Q

What are cross-sectional studies?

A

exposure/intervention and outcomes are measured at the same time – ‘snap-shot’ view

42
Q

What are the advantages of cross-sectional studies?

A
  • simple to carry out, inexpensive
  • can evaluate multiple outcomes
  • can measure outcome prevalence (% with outcome at single time point)
43
Q

What are the disadvantages of cross-sectional studies?

A
  • 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
Q

Comparison of Time in Observational Studies

A
  • cross-sectional study: present
  • case-control study: present to past
  • cohort study: present to future
45
Q

What is the outdated use of retrospective vs. prospective?

A
  • prospective: cohort and randomized trials
  • retrospective: case-control
46
Q

What is the key distinguishing factor of retrospective vs. prospective?

A
  • prospective: exposure measurement cannot be influenced by the outcome
  • retrospective: exposure measurement can be influenced by the outcome
47
Q

What is the updated (better) definition of retrospective vs. prospective?

A
  • prospective: exposure measured/collected prior to the outcome
  • retrospective: exposure measured/collected at the same time/after as the outcome
48
Q

Why do we care about different study designs?

A
  • level of evidence depends on study design
  • each study design is susceptible to different biases
49
Q

List the evidence hierarchy based on quality of evidence, from highest to lowest.

A

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
Q

What is the proposed new evidence-based medicine pyramid?

A
51
Q

What is study registration?

A

involves submitting a study protocol to an online, public access, searchable registry

52
Q

What type of studies is study registration available for?

A

both experimental and observational studies

53
Q

What does study registration do?

A
  • 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
Q

What is a study protocol?

A
  • complete description of PICO/PECO components
  • complete description of the statistical analysis plan
55
Q

What is a reporting guideline?

A

a simple, structured tool for health researchers to use while writing manuscripts

56
Q

What do reporting guidelines do?

A

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
Q

What are the reporting guidelines for randomized trials?

A

Consolidated Standards of Reporting Trials (CONSORT)

58
Q

What are the reporting guidelines for the 3 types of observational studies?

A

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE)

59
Q

What are the reporting guidelines for meta-analyses?

A

Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA)

PHRM 131 (2 decks)

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