IREL 561: Research Methods Fall 2013 Week 10 Based largely on Neuman’s Basics of Social Research, Chapter 8 Prepared by Craig Webster, Ph.D.

2 Questions Appropriate for an Experiment When do you do one?

3 Random Assignment Why assign randomly? How to randomly assign Matching versus random assignment –Putting people in specific groups (for example, delineated by age or gender)

4 Experimental Design Logic The language of experiments The seven parts 1.Treatment or independent variable 2.Dependent variable 3.Pretest 4.Posttest 5.Experimental group 6.Control group 7.Random assignment

5 Types of Design Classical Experimental Design Preexperimental Designs –One-shot case study design –One-group pretest-posttest design –Static group comparison Quasi-experimental and special designs –Interrupted time series –Equivalent time series –Latin square designs –Solomon four-group design –Factorial designs

6 Internal and External Validity Threats to Internal validity –Selection bias –History –Maturation –Testing –Instrumentalization –Mortality –Statistical regression –Diffusion of treatment or contamination –Experimenter expectancy

7 External Validity and Field Experiments Reactivity (the Hawthorne Effect) Field Experiments

8 Practical Considerations Planning and Pilot-Tests Instructions to Subjects Postexperiment Interview