Paula Peyrani, MDInstructor of Medicine
Division of Infectious DiseasesUniversity of Louisville, Kentucky
Planning Your StudyPlanning Your StudyObservational StudiesObservational Studies
Objectives
To describe the study design in observational studies.
• Take a passive or active role in the study.
Planning The StudyPlanning The Study
• Take a passive or active role in the study.
Planning The StudyPlanning The Study
Study Design Key Feature Example
Planning The StudyPlanning The Study
Study Design Key Feature Example
Cohort study A group followed over time
• Women followed yearly for several years.
• Incidence of osteopenia. • Hormone users and non-users.
Planning The StudyPlanning The Study
Study Design Key Feature Example
Cohort study A group followed over time
• Women followed yearly for several years.
• Incidence of osteopenia. • Hormone users and non-users.
Cross-sectional study
A group examined at one point in time
• Women examined once.• Prevalence of h/o osteopenia.• Hormone users and non-users.
Planning The StudyPlanning The Study
Study Design Key Feature Example
Cohort study A group followed over time
• Women followed yearly for several years.
• Incidence of osteopenia. • Hormone users and non-users.
Cross-sectional study
A group examined at one point in time
• Women examined once.• Prevalence of h/o osteopenia.• Hormone users and non-users.
Case-control study Two groups, based on the outcome
• Group of women with osteopenia (cases)
• Group of women without osteopenia (controls)
• Hormone use.
Planning The StudyPlanning The Study
• No approach is better than the other.
Planning The StudyPlanning The Study
• No approach is better than the other.
• Define which study is the best to answer the research question.
Planning The StudyPlanning The Study
• No approach is better than the other.
• Define which study is the best to answer the research question.
• Observational study may be a better choice or the only feasible option
Planning The StudyPlanning The Study
Clinical & Translational Research Clinical & Translational Research
Study: Area/Problem/Question/Objective/HypothesisStudy: Area/Problem/Question/Objective/HypothesisStudy: Area/Problem/Question/Objective/HypothesisStudy: Area/Problem/Question/Objective/Hypothesis
Streptococcus pneumoniae Streptococcus pneumoniae Streptococcus pneumoniae Streptococcus pneumoniae
Beta lactam antibiotic (monotherapy)Beta lactam antibiotic (monotherapy)Beta lactam antibiotic (monotherapy)Beta lactam antibiotic (monotherapy)
Beta lactam plus macrolidesBeta lactam plus macrolidesBeta lactam plus macrolidesBeta lactam plus macrolides
Clinical outcomesClinical outcomesClinical outcomesClinical outcomes
Research IdeaResearch IdeaResearch IdeaResearch Idea
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
Study SubjectsTime OO
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
Postmenopausal womenTime
Estrogen Estrogen treatmenttreatment
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
• Describe the incidence or natural history of a condition.
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
• Describe the incidence or natural history of a condition.
• Analyze predictors (risk factors) for various outcomes.
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Cohort: Roman term for a group of soldiers that marched together
In clinical research, it is a group of subjects followed over time
Planning The StudyPlanning The Study
• Describe the incidence or natural history of a condition.
• Analyze predictors (risk factors) for various outcomes.
• Two basic variations: prospective or retrospective.
Study Designs Study Designs Study Designs Study Designs
Planning The StudyPlanning The Study
Prospective Study
Retrospective Study
Descriptive
Study
Analytical Study
Description vs. cause/effect
Past vs. future outcomes
Passive vs. active role
1. Case report/series2. Cross-sectional study
3. Case-control study4. Cohort study
1. Non-randomized2. Randomized (RCT)
Observational Study
InterventionalStudy
Hierarchy of Evidence
12
3456
Retrospective Retrospective Observational Observational
Descriptive Study Descriptive Study
Retrospective Retrospective Observational Observational Analytic StudyAnalytic Study
Prospective Prospective Randomized Randomized Clinical TrialClinical Trial
Prospective Prospective Observational Observational Analytic StudyAnalytic Study
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Planning The StudyPlanning The Study
Postmenopausal womenTime
Estrogen Estrogen treatmenttreatment
Descriptive studyDescriptive study
Cohort Studies Cohort Studies Cohort Studies Cohort Studies
Planning The StudyPlanning The Study
Postmenopausal womenTime CHDCHD
Analytical studyAnalytical studyOn estrogenOn estrogen
No estrogenNo estrogen
THE PAST
Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective
Planning The StudyPlanning The Study
THE PAST/PRESENT
Risk factor present
Risk factor absent
Population
Sample
Disease No disease
Disease No disease
THE PAST
Planning The StudyPlanning The Study
THE PAST/PRESENT
Normal vitamin D
Low vitamin D
HIV-infected subjects
HIV-infected subjects at UofL
AIDS No AIDS
AIDS No AIDS
Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective
THE PRESENT
Planning The StudyPlanning The Study
THE FUTURE
Use of estrogens
No use of estrogens
Postmenopausal Women
Postmenopausal Women at
UofL
CHD No CHD
CHD No CHD
Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective
Strengths
- Good for investigating causes of a condition - Good for defining incidence - Measures variables completely and accurately- Much less costly and time consuming
THE PRESENT
Planning The StudyPlanning The Study
THE FUTURE
Use of estrogens
No use of estrogens
Postmenopausal Women
Postmenopausal Women at
UofL
CHD No CHD
CHD No CHD
Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective Cohort Studies - Retrospective
Strengths Weakness
- Good for investigating causes of - Limited control over: a condition population sampling- Good for defining incidence quality of variables- Measures variables completely and accurately- Much less costly and time consuming
THE PRESENT
Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective
Planning The StudyPlanning The Study
THE FUTURE
Risk factor present
Risk factor absent
Population
Sample
Disease No disease
Disease No disease
THE PRESENT
Planning The StudyPlanning The Study
THE FUTURE
Use of estrogens
No use of estrogens
Postmenopausal Women
Postmenopausal Women at
UofL
CHD No CHD
CHD No CHD
Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective
THE PRESENT
Planning The StudyPlanning The Study
THE FUTURE
Use of estrogens
No use of estrogens
Postmenopausal Women
Postmenopausal Women at
UofL
CHD No CHD
CHD No CHD
Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective
Strengths
- Good for defining incidence- Good for investigating causes of a condition - Measures variables completely and accurately
THE PRESENT
Planning The StudyPlanning The Study
THE FUTURE
Use of estrogens
No use of estrogens
Postmenopausal Women
Postmenopausal Women at
UofL
CHD No CHD
CHD No CHD
Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective Cohort Studies - Prospective
Strengths Weakness
- Good for defining incidence - Inefficient way to study rare outcomes- Good for investigating causes of a condition - Measures variables completely and accurately
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Planning The StudyPlanning The Study
SubjectsTime
The investigator makes The investigator makes all measurements for all measurements for
each subject in a single each subject in a single occasionoccasion
Cross-sectional study Cross-sectional study Cross-sectional study Cross-sectional study
Planning The StudyPlanning The Study
Population
Sample
Risk factor; Risk factor; Disease No Disease No risk factor; No risk factor; Disease No Disease
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Planning The StudyPlanning The Study
SubjectsTime
MayMay
100 women tested; 12 women diagnosed 100 women tested; 12 women diagnosed
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Incidence
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Cohort study Incidence
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Cohort study Incidence # people who get the disease over time
# people at risk during that time
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Cohort study Incidence # people who get disease over period time
# people at risk during that period
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Strengths
- No waiting for outcome to occur- Fast and inexpensive - No loss to follow-up
Type of Study Statistics Definition
Cross-sectional study
Prevalence # people who have the disease at that point
# people at risk at that point
Cohort study Incidence # people who get disease over period time
# people at risk during that period
Planning The StudyPlanning The Study
Cross-sectional studiesCross-sectional studiesCross-sectional studiesCross-sectional studies
Strengths Weakness
- No waiting for outcome to occur - Difficult to establish causality - Fast and inexpensive - Impractical for the study of rare- No loss to follow-up diseases.
- Limited information on prognosis and natural history
Planning The StudyPlanning The Study
Case-control Studies Case-control Studies Case-control Studies Case-control Studies
Study SubjectsTime OOPP
Planning The StudyPlanning The Study
Case-control Studies Case-control Studies Case-control Studies Case-control Studies
Study SubjectsTime
OO
PP
Planning The StudyPlanning The Study
Case-control Studies Case-control Studies Case-control Studies Case-control Studies
Study SubjectsTime OOPP
CasesCases
ControlsControls
Planning The StudyPlanning The Study
Case-control Studies Case-control Studies Case-control Studies Case-control Studies
Study SubjectsTime OOPP
CasesCases
ControlsControls
Risk factorsRisk factors
THE PAST Case-control StudiesCase-control StudiesCase-control StudiesCase-control Studies
Planning The StudyPlanning The Study
THE PAST/PRESENTPopulation
with disease
Risk factor present
Risk factor absent
Risk factor present
Risk factor absent
Cases
Sample with disease
Larger population without disease
Controls
Sample with disease
THE PASTCase-control StudiesCase-control StudiesCase-control StudiesCase-control Studies
Planning The StudyPlanning The Study
Prior abx use
No prior abx use
Prior abx use
No prior abx use
VAP
due to suscep Acinet
to
VAP due MDR Acinet
THE PAST/PRESENT
THE PASTCase-control StudiesCase-control StudiesCase-control StudiesCase-control Studies
Planning The StudyPlanning The Study
THE PRESENT
Prior abx use
No prior abx use
Prior abx use
No prior abx use
VAP
due to suscep Acinet
to
VAP due MDR Acinet
Strengths
- High yield of information from relatively few subjects- Efficient for diseases with long latent periods- Useful for generating hypothesis.
THE PASTCase-control StudiesCase-control StudiesCase-control StudiesCase-control Studies
Planning The StudyPlanning The Study
THE PRESENT
Prior abx use
No prior abx use
Prior abx use
No prior abx use
VAP
due to suscep Acinet
to
VAP due MDR Acinet
Strengths Weakness
- High yield of information from - Limited information relatively few subjects - Only one outcome can be studied- Efficient for diseases with long - Increased susceptibility to BIAS latent periods- Useful for generating hypothesis
THE PASTCase-control StudiesCase-control StudiesCase-control StudiesCase-control Studies
Planning The StudyPlanning The Study
THE PRESENT
Prior abx use
No prior abx use
Prior abx use
No prior abx use
VAP
due to suscep Acinet
to
VAP due MDR Acinet
Strengths Weakness
- High yield of information from - Limited information relatively few subjects - Only one outcome can be studied- Efficient for diseases with long - Increased susceptibility to BIAS latent periods- Useful for generating hypothesis
Matching: Is a simple method of ensuring that cases and controlsare comparable with respect to
major factors that are related tothe outcome but not of interest to
the investigator
Planning The StudyPlanning The Study
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