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Chapter 10

Rigor and Validity in
Quantitative Research

Validity and Validity Threats

Validity: the approximate truth of inference
Threats to validity are reasons that an inference could be wrong.

Types of Validity

Statistical conclusion validity
Internal validity
Construct validity
External validity

Controlling Intrinsic Source
of Confounding Variability

Randomization
Crossover
Homogeneity
Stratification/blocking
Matching (pair matching)
Statistical control

Benefits and Limitations of Control Methods: Randomization

Benefits:

Controls all preintervention confounding variables
Does not require advance knowledge of which variables to control

Limitations:

Ethical and practical constraints on variables that can be manipulated
Possible artificiality of conditions

Benefits and Limitations of Control Methods: Crossover (Repeated Measures)

Benefits:

If done with randomization, strongest possible approach

Limitations:

Cannot be used if there are possible carryover effects from one condition to another
History threat may be relevant if external factors change over time.

Benefits and Limitations of Control Methods: Homogeneity

Benefits:

Easy to achieve in all types of research
Enhances interpretability of relationships

Limitations:

Limits generalizability
Requires knowledge of which variables to control
Range restriction could lower statistical conclusion validity.

Benefits and Limitations of Control Methods: Stratification

Benefits:

Enhances the ability to detect and interpret relationships
Offers opportunity of examining blocking variable as an independent variable

Limitations:

Usually restricted to a few stratifying variables
Requires knowledge of which variables to control

Benefits and Limitations of Control Methods: Matching

Benefits:

Enhances interpretability of relationships
May be easy if there is a large “pool” of potential available controls

Limitations:

Usually restricted to a few matching variables
Requires knowledge of which variables to match
May be difficult to find comparison group matches, especially if there are more than two matching variables

Benefits and Limitations of Control Methods: Statistical Control

Benefits:

Enhances ability to detect and interpret relationships
Relatively economical means of controlling several confounding variables

Limitations:

Requires knowledge of which variables to control, as well as measurement of these variables
Requires some statistical sophistication

Four Types of Validity Affect
Rigor of Quantitative Study

Statistical conclusion validity
Internal validity
Construct validity
External validity

Statistical Conclusion Validity

Low statistical power
Restriction of range
Unreliable implementation of a treatment

Intervention Fidelity

Extent to which the implementation of a treatment is faithful to its plan

Internal Validity

Temporal ambiguity
Selection
History
Maturation
Mortality/attrition
Testing and instrumentation

Construct Validity

Concerns inferences from the particular exemplars of a study to the higher order constructs that they are intended to represent

Threats to Construct Validity

Reactivity to the study situations
Researcher expectancies
Novelty effects
Compensatory effects
Treatment diffusion

External Validity

Concerns inferences about the extent to which relationships observed in a study hold true over variations in people, conditions, and setting as well as over variations in treatments and outcomes

Threats to External Validity

Interaction between relationship and people
Interaction between causal effects and treatment variation

Trade-Offs and Priorities in Study Validity

Internal and external validity
Prioritization and design decisions

RE-AIM Framework

Reach
Efficacy
Adoption
Implementation
Maintenance