“This book is a must for learning about the experimental design–from forming a research question to interpreting the results this text covers it all.” –Sarah El Sayed, University of Texas at Arlington Designing Experiments for the Social Sciences: How to Plan, Create, and Execute Research Using Experiments is a practical, applied text for courses in experimental design. The text assumes that students have just a basic knowledge of the scientific method, and no statistics background is required. With its focus on how to effectively design experiments, rather than how to analyze them, the book concentrates on the stage where researchers are making decisions about procedural aspects of the experiment before interventions and treatments are given. Renita Coleman walks readers step-by-step on how to plan and execute experiments from the beginning by discussing choosing and collecting a sample, creating the stimuli and questionnaire, doing a manipulation check or pre-test, analyzing the data, and understanding and interpreting the results. Guidelines for deciding which elements are best used in the creation of a particular kind of experiment are also given. This title offers rich pedagogy, ethical considerations, and examples pertinent to all social science disciplines.

Internal and External Validity

No issue . . . has a longer half-life or recurs with more regularity than the argument over the validity and generalizability of findings obtained from social scientific experiments.1

—John A. Courtright

Learning Objectives

  • Illustrate internal and external validity and the trade-offs.
  • Identify how generalizability is achieved in experiments.
  • Compare logical inference versus statistical inference.
  • Discuss the role of replication in experimentation.
  • Explain how random assignment provides internal validity.
  • Identify the seven classes of extraneous variables that jeopardize internal validity.

The previous chapter looked at different kinds of experiments—lab or true, quasi, natural, and field—and concluded there is no perfect experiment. As in life, experiments involve trade-offs, and that is especially true of the two sides of validity—external and internal. Like children on a seesaw, one type of validity ...

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