Chapter 9 enhancing rigor in quantitative research
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Chapter 9 Enhancing Rigor in Quantitative Research. Controlling Extraneous Variables. Controlling external, situational factors—constancy of conditions. Constancy of the environment Constancy of treatment conditions Constancy of time Constancy of communications to subjects.

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Chapter 9 enhancing rigor in quantitative research

Chapter 9Enhancing Rigor in Quantitative Research


Controlling extraneous variables
Controlling Extraneous Variables

Controlling external, situational factors—constancy of conditions

  • Constancy of the environment

  • Constancy of treatment conditions

  • Constancy of time

  • Constancy of communications to subjects


Controlling intrinsic subject characteristics
Controlling Intrinsic Subject Characteristics

  • Randomization

  • Repeated measures

  • Homogeneity

  • Blocking

  • Matching/balancing

  • Statistical control



Benefits and limitations of control methods randomization
Benefits and Limitations of Control Methods: Randomization

Benefits:

  • Controls all extraneous variables

  • Does not require advance knowledge of which variables to control

    Limitations:

  • Ethical and practical constraints on manipulation

  • Possible artificiality of conditions


Benefits and limitations of control methods repeated measures
Benefits and Limitations of Control Methods: Repeated Measures

Benefits:

  • If done with randomization, strongest possible approach

  • Reduces sample size requirements

    Limitations:

  • Cannot be used if there are possible carry-over effects from one condition to another


Benefits and limitations of control methods homogeneity
Benefits and Limitations of Control Methods: Homogeneity Measures

Benefits:

  • Easy to achieve

  • Enhances interpretability of relationships

    Limitations:

  • Limits generalizability

  • Requires knowledge of which variables to control


Benefits and limitations of control methods blocking
Benefits and Limitations of Control Methods: Blocking Measures

Benefits:

  • Enhances interpretability of relationships

  • Offers possibility of examining blocking variable as an independent variable

    Limitations:

  • Manageable only with a few blocking variables

  • Requires knowledge of which variables to control


Benefits and limitations of control methods matching
Benefits and Limitations of Control Methods: Matching Measures

Benefits:

  • Enhances interpretability of relationships

  • Easy to do if there is a large pool of available comparison group subjects

    Limitations:

  • Manageable only with a few matching variables

  • Requires knowledge of which variables to control

  • May be hard to find comparison group matches


Benefits and limitations of control methods statistical control
Benefits and Limitations of Control Methods: Statistical Control

Benefits:

  • Enhances interpretability of relationships

  • Easy and economical

  • Can be used with a large number of extraneous variables

    Limitations:

  • Requires knowledge of which variables to control

  • Requires statistical sophistication


Characteristics of good research design in quantitative studies
Characteristics of Good Research Design in Quantitative Studies

  • Statistical conclusion validity

  • Internal validity

  • External validity

  • Construct validity


Threats to statistical conclusion validity
Threats to Statistical Conclusion Validity Studies

  • Low statistical power

  • Inadequate precision

  • Unreliable implementation of a treatment

  • Inadequate participation in treatment conditions


Problems with treatment implementation analytic options
Problems with Treatment Implementation: Analytic Options Studies

Analytic strategies when subjects withdraw from study or fail to get full exposure to treatment:

  • On protocol analysis

  • Intention to treat principle

  • Analysis of “dose” of treatment received


Threats to internal validity
Threats to Internal Validity Studies

  • History

  • Selection

  • Maturation

  • Testing

  • Instrumentation

  • Mortality



Accessible vs target population
Accessible vs. Target Population Studies

Accessible population:

The population available for a particular study

Target population:The total group of people in whom a researcher is interested and to whom results could be generalized


Threats to external validity
Threats to External Validity Studies

  • Inadequate sampling

  • Expectancy effects

  • Novelty effects

  • Interaction of history and treatment effects

  • Experimenter effects

  • Measurement effects


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