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?

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

What is blinding?

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

What are the two types of blinding?

<p>Single and double blinding.</p> Signup and view all the answers

What is single blinding?

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

What is double blinding?

<p>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.</p> Signup and view all the answers

What is the meaning of a placebo-controlled experiment?

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

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

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

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

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

What is the sample size in the CARDS study?

<p>The sample is the 2838 subjects in the study.</p> Signup and view all the answers

What are the treatments in the CARDS study?

<p>10 mg of Lipitor or a placebo daily.</p> Signup and view all the answers

What is the response variable in the CARDS study?

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

What are the 6 steps to design an experiment?

<p>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.</p> Signup and view all the answers

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

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

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

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

Explain Step 3: Determine the Number of Experimental Units.

<p>Choose as many experimental units as time and money allow.</p> Signup and view all the answers

What are the two ways to deal with factors?

<p>Randomize and control.</p> Signup and view all the answers

What does it mean to randomize factors?

<p>Randomly assign the experimental units to treatment groups.</p> Signup and view all the answers

What is replication in an experiment?

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

What is done in Step 5 Conduct the Experiment?

<p>Replication and collect and process the data.</p> Signup and view all the answers

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

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

What is inferential statistics?

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

What is a completely randomized design?

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

What is a matched-pairs design?

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

What is treatment?

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

What is a response variable?

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

What is confounding?

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

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

<p>randomized</p> Signup and view all the answers

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

<p>matched</p> Signup and view all the answers

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

<p>observational study</p> 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.

<p>True (A)</p> Signup and view all the answers

Flashcards

Experiment

A controlled study where a controlled variable is changed to observe its impact on a response variable.

Treatment

Specific values or combinations of factors applied to different experimental units during an experiment.

Experimental Unit

The individual item or subject that receives a treatment in an experiment.

Subject (in human studies)

The term used for an experimental unit when it's a person participating in a study.

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Response Variable

The variable measured to see how it's affected by different treatments.

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Goal of an Experiment

To understand how different treatments influence the chosen response variable.

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Control Group

A group that doesn't receive the treatment, serving as a baseline for comparison.

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Blinding

Hiding information about treatment allocation from subjects or researchers to reduce bias.

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Single Blinding

Subjects are unaware of the treatment they're receiving.

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Double Blinding

Both subjects and researchers are unaware of treatment allocation.

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CARDS Study

A double-blind, placebo-controlled study investigating Lipitor's effect on cardiovascular disease in type 2 diabetes patients.

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Identifying the Problem

Clarifying the response variable and the population to be studied.

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Factors Affecting the Response

Identifying variables that might influence the response variable, deciding which to manipulate, control, or observe.

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Sample Size

The number of experimental units needed for reliable results, considering resources and desired precision.

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Factor Levels

The different values or settings assigned to each factor during the experiment.

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Replication

Repeating the experiment multiple times with different experimental units to ensure results aren't due to chance.

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Randomization

Assigning experimental units to treatments randomly to minimize the influence of uncontrolled variables.

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Control

Setting factors at fixed or varying levels to minimize their influence on results.

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Data Collection

Recording the response variable values for each experimental unit in each treatment group.

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Data Processing

Organizing and analyzing the collected data to compare the effects of different treatments.

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Inferential Statistics

Drawing conclusions about a larger population based on the results of a sample from that population.

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Completely Randomized Design

Experimental units are randomly assigned to different treatment groups.

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Matched-Pairs Design

Experimental units are paired based on similar characteristics, and each pair receives different treatments.

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Quantitative Response Variable

A response variable that can be measured numerically.

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Qualitative Response Variable

A response variable that describes categories or qualities.

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Confounding

When the effects of two explanatory variables on the response variable are mixed up and can't be separately identified.

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Causality

The relationship between two variables where one causes a change in the other.

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Observational Study

Study where researchers observe and collect data without directly manipulating any variables.

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True or False: The goal of an experiment is to explore the effects of treatments on response variables.

True. The main purpose of an experiment is to observe how different treatments impact a specific response variable.

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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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