Chapter 7 Experimental Design I—Independent Variables - PowerPoint Presentation

399 views
Uploaded On 2018-03-19

Chapter 7 Experimental Design I—Independent Variables - PPT Presentation

The Research Process Evidencebased practice Search for answers Design and development of a study Funding Human and animal use approval Pilot studies Preliminary data Conduct of the study Collection of the data ID: 657070

wolters kluwer 2016 rights kluwer wolters rights 2016 reserved independent design copyright group variables research experimental variable subject subjects

Link:

Copy

Embed:

<iframe width="560" height="315" src="https://www.docslides.com/embed/657070" frameborder="0" allowfullscreen></iframe>

Download Presentation from below link

Download Presentation The PPT/PDF document "Chapter 7 Experimental Design I—Indepe..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.

Presentation Transcript

Slide1

Chapter 7

Experimental Design I—Independent VariablesSlide2

The Research Process

Evidence-based practice

Search for answers

Design and development of a study

Funding

Human and animal use approval

Pilot studiesPreliminary data

Conduct of the study

Collection of the data

Laboratory analysis of data

Statistical analysis of data

Manuscript preparation

Peer review

Publication of manuscript

The Body of KnowledgeAnecdotal observationsScientific literature base

If found

If not found

If rejected

If acceptedSlide3

Key Terms

Alternate/research hypothesis

Between-group/-subject independent variableBiasBlindConfounding or intervening variableConstant

Control group

CounterbalancingDependent variableDouble blindExclusion criteriaExperimental researchExternal validityHawthorne effectInclusion criteriaIndependent variableInternal validityMultivariateNon-experimental researchNull hypothesisPlacebo effectPowerQuasi-experimental researchResearch designTreatment/interventionUnivariateVariableWithin-group/-subject independent variable

Planning the Research Design

Research design is the process by which investigators determine how to answer their research question(s)

Flaws in research design typically cannot be overcome by editing or statistical analysis4

Identifying Variables

A variable is some characteristic or factor that can have different values and is either subject to change or can be manipulated as an intervention

Variables may be independent, dependent, constant, or confounding5

Identifying Variables

Independent Variables: Levels

Examining the effects of different doses of a drug or supplement is an example of multiple levels of a single independent variable

How different doses affect male and female mice is an example of multiple independent variablesFig. 7-1Slide8

Independent Variables: Types

Between-group (or between-subjects) independent variable

: different group of subjects for each level of the variableWithin-group (or within-subject) independent variable: each subject is tested at each level of the independent variableFig. 7-1Slide9

Identifying Variables

Overview of Research Design Dimensions

Design

Primary UseRandomized?

Degree of Control

Retrospective or Prospective?Emphasis on ValidityNon-ExperimentalDescription, examine relationshipsNoLowEitherQuasi-ExperimentalCausal inferencesNoLow/moderateEitherExternalTrue ExperimentalCausal inferencesYesHighProspectiveInternal

Experimental Design: Control Group

Control group: measured

at the same time points as the treatment group(s) but receives no treatmentPlacebo: dummy treatment that does not affect the dependent variable(s)Blinding

: keeping participants (single blind) and ideally both participants and study personnel (double blind) naïve to the study treatment

Experimental Design: Control Group

Placebo effect: subjects receiving the placebo may experience a benefit even though they aren’t receiving any treatment

Hawthorne effect: subjects may perform better due to being observed

Experimental Design: Selecting Subjects

Identify the study population, and obtain a representative sample

Weigh the ability to improve retention (convenience sample) against having a more representative sampleThe degree to which the sample represents the population of interest affects the power of the study

Inclusion criteria are the stated subject characteristics

Experimental Design: Controlling Variability & Bias

Using randomization

or matching to assign subjects to groups reduces other factors affecting the dependent variableControlling for confounding or intervening variables reduces threats to

internal validity

Minimizing signal-to-noise ratio better enables the impact of the independent variable on the dependent variable to be observed Systematic errors occur when measurement error is in one directionRandom errors may occur in any direction and typically have a net zero effect14Copyright © 2016 Wolters Kluwer • All Rights ReservedSlide15

Summary

Research design requires balance, weighing the pros and cons of a number of experimental choices

There is a trade-off between controlling variables and real-world applicability Planning is key for avoiding confounding factors