DrugEpi 3-5 Fundamentals of Study Design Module 3 Introduction Content Area: Analytical Epidemiology...

DrugEpi 3-5 Fundamentals of Study Design

Module 3 IntroductionContent Area: Analytical EpidemiologyEssential Question (Generic): Is there an association between the hypothesized cause and the disease?Essential Question (Drug Abuse Specific): Is there an association between the hypothesized cause and drug use?Enduring Epidemiological Understanding: Causal hypotheses can be tested by observing exposures and diseases of people as they go about their daily lives. Information from these observational studies can be used to make and compare rates and identify associations.

Synopsis

In Module 3, students explore how hypotheses are tested epidemiologically. Students begin to uncover and develop the following epidemiological concepts and skills: the meaning of the term “association;” the need for a control group; uses of the 2x2 table in calculating risks and relative risks; experimental study design; the importance of ethics in human research; observational study designs used in epidemiology; and the strengths and limitations of each design.

Lesson 3-1: Associations and the 2x2 TableLesson 3-2: Experimental Study - Buprenorphine ExampleLesson 3-3: An Actual Randomized Controlled TrialLesson 3-4: Observational Studies of Natural Experiments - Sensation-Seeking ExampleLesson 3-5: Fundamentals of Study DesignLesson 3-6: Study Design Exercises


Module 3 - Analytical Epidemiology

Lesson 3-5 Fundamentals of Study Design

Content

• Introduction to concepts of epidemiology study designs• Overview of the four main study designs used in epidemiology: 1) controlled trial;

2) cohort study; 3) case-control study; and 4) cross-sectional study• Ways of explaining the flow of each study design, in text and visually• The uncovering of the strengths and limitations of each design• Examples of how each design can be applied to evaluating the effectiveness of

student drug testing programs• Practice in identifying each study design

Big Ideas

• Each study design can be expressed in a 2x2 table format • Each study design has a different plan for assessing exposure and disease• The experimental design is the most scientifically rigorous and the observational

study designs vary in rigor from quite good to poor• There is a trade-off between scientifically stronger studies that take more effort

and money to conduct well, and the less scientific studies that are “quicker and dirtier”

This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse,

National Institutes of Health.


1. How is this disease distributed?

Health-related conditions and behaviors are not distributed uniformly in a population. They have unique distributions that can be described by how they are distributed in terms of person, place, and time.

2. What hypotheses might explain the distribution of disease?

Clues for formulating hypotheses can be found by observing the way a health-related condition or behavior is distributed in a population.

3. Is there an association between the hypothesized cause and the disease?

Causal hypotheses can be tested by observing exposures and diseases of people as they go about their daily lives. Information from these observational studies can be used to make and compare rates and identify associations.

4. Is the association causal? Causation is only one explanation for an association between an exposure and a disease. Because observational studies are complicated by factors not controlled by the observer, other explanations also must be considered.

5. What should be done when preventable causes of disease are found?

Policy decisions are based on more than the scientific evidence. Because of competing values - social, economic, ethical, environmental, cultural, and political factors may also be considered.

Essential Questions Enduring Understandings

Where are we?


The Journey


Descriptive Epidemiology

Describes those who have the outcome (PPT)

Generates hypotheses

Surveillance: A way to obtain descriptive information – Example: National Survey on Drug Use and Health

Review – What is in your epidemiology Toolbox so far?

DZ

DZ

DZ

DZ


Exposed

Not Exposed

DiseaseNo

Disease TotalTests hypotheses

Needs an unexposed comparison group

Uses the 2x2 table to calculate rates and compare risks in exposed/unexposed

However . . .

The 2x2 table does not show how the study was done (study design does this)

Analytic Epidemiology . . .

Review – What is in your epidemiology Toolbox so far?


Procedures and methods, established beforehand, that are followed by the investigators

conducting the study

This Lesson


CDC

This will all make sense to you!

There are four basic study designs for testing hypotheses.

Each design has a different plan for assessing exposure and disease.

The plan for each design can be understood by constructing a flow diagram.

Whatever the study design and its flow diagram, it can be “fit” into a 2x2 table so that risks can be calculated and compared (RR).

Preview


Four Basic Study Designs

Controlled Trial

Cohort

Case-Control

Cross-Sectional

Observational

Experimental


Controlled Trial (a planned experiment)

An epidemiologic experiment in which subjects are assigned into groups to receive or not receive a hypothesized beneficial intervention.

Examples in Lessons 3-2 and 3-3: Buprenorphine in the treatment of heroin addiction

Review of Important Concepts


Epidemiologist

Board of Education

Hypothesis: Smoking marijuana causes memory loss.

Research suggests a relationship

between poor grades and

drug use

Scenario


200 High School Students

No

Marijuana

100 StudentsControl

Group

Marijuana

100 StudentsExperimental

Group4 Months

Measure Memory Loss

2 x 2 Table, Calculate Risks, and Relative Risk

What’s wrong with this picture?

Measure Memory

Scenario


Natural Experiment (unplanned)

Naturally occurring circumstances in which groups of people within a population have been exposed to different levels of the hypothesized cause of an outcome.

Review of Important Concepts


Observational Studies of Natural Experiments

A study in which the investigator does not decide who will and will not be exposed and to how much, but rather, observes what exposures occur in free-living people.

Important Concepts

Examples in Lesson 3-4: Sensation-seeking and high risk behaviors


The Journey


Analogy


Reminder

Procedures and methods, established beforehand,

that are followed by the investigators conducting the study


CDC

-

Epidemiologists = Medical Detectives


When are the passengers identified as exposed or unexposed?

E

When are the passengers identified as sick or not sick?

DZ

Timing

When does the epidemiologist start to observe the journey?

Study Design – Timing Is Everything


Time

E DZ

It helps to “see” what is happening

Studying the Journey


As the train journey begins, the epidemiologist gives the exposure to randomly selected passengers and does not give it to the other passengers. The epidemiologist stays on the train during the entire journey and continues to give the exposure to the randomly selected passengers. Throughout the train ride, the epidemiologist keeps track of all passengers (exposed and unexposed) to record which ones develop the disease during the journey.

Design # 1 Controlled Trial (Experimental)


What’s Happening?


E


DZ


Study Design: Controlled Trial

E DZ+++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++

Time


Healthy People

Controlled

Trial

Flow Diagram

E

Random Assignment

E

DZ

DZ

DZ

DZ

Controlled Trial Flow Diagram

Time


Healthy People

Controlled

Trial

Flow Diagram

E

Random Assignment

E

DZ

DZ

DZ

DZ

Evaluating a Student Drug Testing Program

Time


Healthy People

Randomized

Controlled

Trial


Time


Observational Studies of Natural Experiments

A study in which the investigator does not decide who will and will not be exposed and to how much, but rather, observes what exposures occur in free-living people.

Reminder


Just as in the controlled trial, the epidemiologist is on the train during the entire journey. But there is an important difference. The epidemiologist is not telling passengers what to do. Rather, the epidemiologist is just observing them and counting. Passengers are not being told to have or not have an exposure, they are just living their normal lives. The epidemiologist, on the ride for the whole journey, just keeps observing everyone’s exposures and whether or not they develop the disease during the journey.

Design # 2 - Cohort Study


Study Design: Cohort Study

What’s Happening?


E


DZ


DZ+++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++

E

Time


Cohort

Study

Flow Diagram

E

E

DZ

DZ

DZ

DZ

Cohort Study Flow Diagram

Healthy PeopleHealthy People

Time


Healthy People

Cohort

Study

Flow Diagram

Healthy People

E

E

DZ

DZ

DZ

DZ

Controlled

Trial

Similarities

Time


Healthy People

Cohort

Study

Flow Diagram

Healthy People

E

E

DZ

DZ

DZ

DZ

Controlled

Trial

Random Assignment

Difference

Time


Cohort

Study

Flow Diagram

E

E

DZ

DZ

DZ

DZ



Time


Cohort

Study

Flow Diagram



Time


The epidemiologist is not on the journey. Rather, the epidemiologist is waiting at the train station at the end of the journey. As passengers get off the train, the epidemiologist selects sick passengers for the case group and selects passengers who are similar but not sick for the control group. The epidemiologist then asks each person in the case group and control group questions about their exposures during the train ride. The epidemiologist relies on passengers’ memories of their exposures that occurred during the train ride.

Design # 3 - Case-Control Study


What’s Happening?


E


DZ


Study Design: Case-Control Study

EDZ

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Time


Case-Control

Study

Observational

Study

Flow Diagram

Time

DZ

DZ

E

E

E

E

Case-Control Study Flow Diagram


Case-Control

Study

Observational

Study

Flow Diagram

Time

DZ

DZ

E

E

E

E



Case-Control

Study

Observational

Study

Flow Diagram

Time



The epidemiologist, who has not been on the journey, stops the train somewhere during the trip (kind of like a train robbery) and takes a “snapshot” of all the passengers by asking them whether or not they had the exposure and whether or not they have the disease. Then the epidemiologist leaves the train and goes home to analyze the data from that particular day. The journey continues without the epidemiologist.

Design # 4 - Cross-Sectional Study


What’s Happening?


E



Study Design: Cross-Sectional Study

Time

DZ

EDZ

+++++++++++++++++++++++++++ ++++++++++++++++++++++++ +++++++++++++++++++++++++ +++++++++++++++++++++++


Cross-Sectional

Study

Observational

Study

Flow Diagram

E

E

DZ

DZ

Cross-Sectional Study Flow Diagram

Time


Cross-Sectional

Study

Observational

Study

Flow Diagram

E

E

DZ

DZ


Time


Cross-Sectional

Study

Observational

Study

Flow Diagram


Time


Controlled Trial

Cohort Study

Case-Control

Cross-Sectional

Observational

Experimental

Summary

DrugEpi 3-5 Fundamentals of Study DesignTime

Four Ways to Study the Journey

E DZTrial+++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++

EDZ

Case-Control Study++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

EDZ

+++++++++++++++++++++++++++ ++++++++++++++++++++++++ +++++++++++++++++++++++++ +++++++++++++++++++++++

Cross-Sectional Study

DZ+++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++

E Cohort Study


Controlled Trial

Cohort Study

Case-Control Study

Cross-Sectional Study


E

Random Assignment

E

DZ

DZ

DZ

DZ


E

E

DZ

DZ

DZ

DZ

DZ

DZ

E

E

E

E

E

E

DZ

DZ

The Four Study Designs


CDC

Does this all make sense

to you?

There are four basic study designs for testing hypotheses.

Each design has a different plan for assessing exposure and disease.

The plan for each design can be understood by constructing a flow diagram.

Whatever the study design and its flow diagram, it can be “fit” into a 2x2 table so that risks can be calculated and compared (RR).

Making Sense


Big Ideas in this Lesson (3-5)

•Each study design can be expressed in a 2x2 table format

•Each study design has a different plan for assessing exposure and disease

•The experimental design is the most scientifically rigorous and the observational study designs vary in rigor from quite good to poor

•There is a trade-off between scientifically stronger studies that take more effort and money to conduct well, and the less scientific studies that are “quicker and dirtier”

This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse,

National Institutes of Health.

Re-Cap


6.

Where are we?Next Lesson

Learn more about epidemiology study designs in

Epi Team Challenges

DrugEpi 3-5 Fundamentals of Study Design Module 3 Introduction Content Area: Analytical Epidemiology...

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