Paula Peyrani, MD Instructor of Medicine Division of Infectious Diseases

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

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.







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.


• No approach is better than the other.



• Define which study is the best to answer the research question.



• Define which study is the best to answer the research question.

• Observational study may be a better choice or the only feasible option


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






Study SubjectsTime OO





Postmenopausal womenTime

Estrogen Estrogen treatmenttreatment





• Describe the incidence or natural history of a condition.






• Analyze predictors (risk factors) for various outcomes.






• Analyze predictors (risk factors) for various outcomes.

• Two basic variations: prospective or retrospective.

Study Designs Study Designs Study Designs Study Designs


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



Postmenopausal womenTime

Estrogen Estrogen treatmenttreatment

Descriptive studyDescriptive 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


THE PAST/PRESENT

Risk factor present

Risk factor absent

Population

Sample

Disease No disease

Disease No disease

THE PAST


THE PAST/PRESENT

Normal vitamin D

Low vitamin D

HIV-infected subjects

HIV-infected subjects at UofL

AIDS No AIDS

AIDS No AIDS


THE PRESENT


THE FUTURE

Use of estrogens

No use of estrogens

Postmenopausal Women

Postmenopausal Women at

UofL

CHD No CHD

CHD No CHD


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


THE FUTURE

Use of estrogens

No use of estrogens



UofL

CHD No CHD

CHD No CHD


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


THE FUTURE

Risk factor present

Risk factor absent

Population

Sample

Disease No disease

Disease No disease

THE PRESENT


THE FUTURE

Use of estrogens

No use of estrogens



UofL

CHD No CHD

CHD No CHD


THE PRESENT


THE FUTURE

Use of estrogens

No use of estrogens



UofL

CHD No CHD

CHD No CHD


Strengths

- Good for defining incidence- Good for investigating causes of a condition - Measures variables completely and accurately

THE PRESENT


THE FUTURE

Use of estrogens

No use of estrogens



UofL

CHD No CHD

CHD No CHD


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


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


Population

Sample

Risk factor; Risk factor; Disease No Disease No risk factor; No risk factor; Disease No Disease



SubjectsTime

MayMay

100 women tested; 12 women diagnosed 100 women tested; 12 women diagnosed

Type of Study Statistics Definition


Prevalence # people who have the disease at that point

# people at risk at that point







Incidence







Cohort study Incidence







Cohort study Incidence # people who get the disease over time

# people at risk during that time







Cohort study Incidence # people who get disease over period time

# people at risk during that period



Strengths

- No waiting for outcome to occur- Fast and inexpensive - No loss to follow-up





Cohort study Incidence # people who get disease over period time

# people at risk during that period



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


Case-control Studies Case-control Studies Case-control Studies Case-control Studies

Study SubjectsTime OOPP



Study SubjectsTime

OO

PP




CasesCases

ControlsControls




CasesCases

ControlsControls

Risk factorsRisk factors

THE PAST Case-control StudiesCase-control StudiesCase-control StudiesCase-control Studies


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


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 PRESENT

Prior abx use

No prior abx use

Prior abx use

No prior abx use

VAP


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 PRESENT

Prior abx use

No prior abx use

Prior abx use

No prior abx use

VAP


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 PRESENT

Prior abx use

No prior abx use

Prior abx use

No prior abx use

VAP


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

Paula Peyrani, MD Instructor of Medicine Division of Infectious Diseases

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