Design of Experiments Flashcards 1.6

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Questions and Answers

What is an experiment?

An experiment is a controlled study conducted to determine the effect varying one or more explanatory variables or factors has on a response variable.

What is an experimental unit?

In an experiment, the experimental unit is a person, object, or some other well-defined item upon which a treatment is applied.

What is the goal of an experiment?

To determine the effect various treatments have on the response variable.

What is a control group?

A control group serves as a baseline treatment that can be used to compare it to other treatments. Signup and view all the answers

What is blinding?

Blinding refers to nondisclosure of the treatment an experimental unit is receiving. Signup and view all the answers

What are the two types of blinding?

Single and double blinding. Signup and view all the answers

What is single blinding?

In single-blind experiments, the experimental unit (or subject) does not know which treatment he or she is receiving. Signup and view all the answers

What is double blinding?

In double-blind experiments, neither the experimental unit nor the researcher in contact with the experimental unit knows which treatment the experimental unit is receiving. Signup and view all the answers

What is the meaning of a placebo-controlled experiment?

The placebo control group serves as a baseline against which to compare the results from the group receiving the treatment. Signup and view all the answers

What does it mean for a study to be double-blind?

Neither the experimental unit nor the researcher knows which treatment is being given. Signup and view all the answers

What is the population for which the Collaborative Atorvastatin Diabetes Study (CARDS) applies?

Individuals from 40 to 75 years of age with type 2 diabetes without a prior history of cardiovascular disease. Signup and view all the answers

What is the sample size in the CARDS study?

The sample is the 2838 subjects in the study. Signup and view all the answers

What are the treatments in the CARDS study?

10 mg of Lipitor or a placebo daily. Signup and view all the answers

What is the response variable in the CARDS study?

Whether the subject had any major cardiovascular event, such as a stroke, or not. Signup and view all the answers

What are the 6 steps to design an experiment?

Step 1 Identify the Problem to Be Solved, Step 2 Determine the Factors That Affect the Response Variable, Step 3 Determine the Number of Experimental Units, Step 4 Determine the Level of Each Factor, Step 5 Conduct the Experiment, Step 6 Test the Claim. Signup and view all the answers

What does Step 1 'Identify the problem to be solved' include?

The statement of the problem should be as explicit as possible and should provide the experimenter with direction. Signup and view all the answers

Explain Step 2: Determine the Factors That Affect the Response Variable.

The factors are usually identified by an expert in the field of study. After identifying, determine which factors to fix, manipulate, and leave uncontrolled. Signup and view all the answers

Explain Step 3: Determine the Number of Experimental Units.

Choose as many experimental units as time and money allow. Signup and view all the answers

What are the two ways to deal with factors?

Randomize and control. Signup and view all the answers

What does it mean to randomize factors?

Randomly assign the experimental units to treatment groups. Signup and view all the answers

What is replication in an experiment?

Replication occurs when each treatment is applied to more than one experimental unit. Signup and view all the answers

What is done in Step 5 Conduct the Experiment?

Replication and collect and process the data. Signup and view all the answers

What does 'collect and process the data' in Step 5 involve?

Measure the value of the response variable for each replication and organize the results. Signup and view all the answers

What is inferential statistics?

Inferential statistics is a process in which generalizations about a population are made on the basis of results obtained from a sample. Signup and view all the answers

What is a completely randomized design?

A completely randomized design is one in which each experimental unit is randomly assigned to a treatment. Signup and view all the answers

What is a matched-pairs design?

A matched-pairs design is an experimental design in which the experimental units are paired up based on a certain criterion. Signup and view all the answers

What is treatment?

Any combination of the values of the factors (explanatory variables). Signup and view all the answers

What is a response variable?

A quantitative or qualitative variable that represents the variable of interest. Signup and view all the answers

What is confounding?

The effect of two factors (explanatory variables) on the response variable cannot be distinguished. Signup and view all the answers

A(n) ____________ design is one in which each experimental unit is randomly assigned to a treatment.

randomized Signup and view all the answers

A(n) ____________ design is one in which the experimental units are paired up.

matched Signup and view all the answers

In an _ __, if an association exists between an explanatory variable and response variable the researcher cannot claim causality.

observational study Signup and view all the answers

True or False: The goal in an experiment is to determine the effect various treatments have on the response variable.

True Signup and view all the answers

Study Notes

Experiment Overview

An experiment is a controlled study to assess the impact of changing explanatory variables on a response variable.
Treatments are specific combinations of factor values applied during the experiment.

Experimental Units

Experimental units are well-defined items (people, objects) that receive treatments. In human studies, these units are referred to as subjects.

Goals of Experiments

The primary goal is to ascertain how different treatments influence the chosen response variable.

Control Group

Control groups serve as baseline comparatives for other treatment groups to evaluate treatment effects.

Blinding

Blinding is the practice of withholding information about treatment allocation from experimental units to minimize bias.
Two blinding types exist: single blinding (subjects unaware of treatment) and double blinding (both subjects and researchers unaware).

Lipitor Study Example

The Collaborative Atorvastatin Diabetes Study (CARDS) evaluated Lipitor's effect on cardiovascular disease in 2838 subjects aged 40-75 with type 2 diabetes.
It was a double-blind, placebo-controlled study comparing Lipitor 10 mg daily to a placebo over four years.
Response variable: occurrence of major cardiovascular events and associated mortality rates.

Steps for Designing an Experiment

Identifying the problem should clarify the response variable and targeted population.
Factors affecting the response variable should be determined, distinguishing which to manipulate or control.
Sample size should be sufficient to ensure reliable results while considering resource limitations.
Determine necessary levels for each factor, controlling their influence as needed.
Conduct experiments with replication and proper data processing to ensure validity.

Randomization and Control

Randomizing experimental units mitigates the influence of uncontrolled variables by evenly distributing them across treatment groups.
Controlling factors involves setting them at fixed or varied levels based on their expected effects.

Replication

Replication ensures treatment effects are not due to random chance by applying each treatment to multiple experimental units.

Data Collection and Processing

Collect data on response variable values for each replication, organizing results to contrast treatment effects.

Inferential Statistics

Inferential statistics involve deriving population generalizations from sample results.

Experimental Designs

Completely randomized design: all experimental units randomly assigned to treatments.
Matched-pairs design: experimental units paired based on related characteristics, with each unit receiving different treatments.

Response Variables

Can be either quantitative or qualitative, representing the main variable of interest.

Confounding

Confounding occurs when the effects of two explanatory variables on the response variable cannot be separately identified.

Causality

Observational studies cannot establish causation between variables; experiments are necessary to determine causal relationships.

True or False Statement

The goal of an experiment is indeed to explore the effects of treatments on response variables.

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Description

Test your understanding of the fundamentals of experimental design with these flashcards. Each card introduces key concepts such as what constitutes an experiment and the role of experimental units. Perfect for anyone studying research methods or statistics.