MORE ON EXPERIMENTS CONFOUNDING OBSCURING VARIABLES Chapter 11

MORE ON EXPERIMENTS: CONFOUNDING & OBSCURING VARIABLES Chapter 11

Learning Objectives Identify 12 potential threats to internal validity Describe how researchers can design studies to prevent internal validity threats Interrogate an experiment with a null result to decide whether the study design obscured an effect or whethere is truly no effect to find Describe how researchers can design studies to minimize possible obscuring factors

Outline 1. Threats to Internal Validity: Did the IV Really Cause the Difference? 2. Interrogating Null Effects: What if the IV Does Not Make a Difference?

1. Threats to Internal Validity: Did the IV Really Cause the Difference? A. B. C. D. The Really Bad Experiment Six Potential Internal Validity Threats in One-Group, Pretest/Posttest Designs Three Potential Internal Validity Threats in Any Study With So Many Threats, Are Experiments Still Useful?

Internal Validity Threats In Chapter 10 we discussed 3 of the most common threats to internal validity � Design confounds � Selection effects � Order effects In this chapter, we will discuss 9 more threats to internal validity

1 A. The Really Bad Experiment Please read the 3 examples of “the really bad experiment” provided in your text book (pp. 312 – 313) All 3 use a one-group, pretest-posttest design