Chapter 9: Conducting Experiments

Selecting Research Participants Most research projects involving sampling research participants from a population of interest. Use probability sampling when it is important to describe the population - Scientific polls

Selecting Research Participants A great deal of research is interested in testing hypotheses about behavior. Participants may be found in the easiest way possible using haphazard or “convenience” sampling methods. Generalization of results - Sample sizes needed

Manipulating the Independent Variable To manipulate an independent variable Turn a conceptual variable into a set of operations (operational definition) - Setting the stage 1. Provide informed consent information 2. Explain why the experiment is being conducted

Manipulating the Independent Variable (con’t) Types of manipulations Straightforward manipulations Staged manipulations

Manipulating the Independent Variable (con’t) Straightforward manipulations Written instructions Verbal material Visual material

Manipulating the Independent Variable (con’t) Staged manipulations Often employ confederates Events are staged or manipulated to: 1. Create some psychological state 2. Simulate some situation that occurs in the real world

Manipulating the Independent Variable (con’t) Strength of the manipulation

Manipulating the Independent Variable (con’t) Importance of a strong manipulation Rare situations Ethics Importance of a manipulation check

Manipulating the Independent Variable (con’t) Cost of the manipulation Participants run individually versus groups Straightforward versus staged manipulations

Measuring the Dependent Variable Types of measures Self-report measures Behavioral measures Physiological measures

Measuring the Dependent Variable (con’t) Sensitivity of the dependent variable Ceiling effect Floor effect

Measuring the Dependent Variable (con’t) Multiple measures Measure more than one dependent variable - A variable can be measured a variety of ways. - If the IV has the same effect on several measures of the same dependent variable, confidence in the results increases ** Question of order arises………..

Measuring the Dependent Variable (con’t) Cost of measures Ethics

Additional Controls Controlling for participant expectations Demand characteristics – use deception Cover story Filler items - Ask participants their perceptions about the purpose of the study

Additional Controls (con’t) Placebo groups Single-blind experiment Placebo effect Balanced placebo design Placebo control groups and ethical considerations

Additional Controls (con’t) Controlling for experimenter expectations Experimenter bias Research on expectancy effects Clever Hans Teacher expectancy (Rosenthal & Jacobsen, 1968)

Additional Controls (con’t) Solutions to the experimenter expectancy problem Experimenter training Run all conditions simultaneous Automate the procedures Double-blind study

Additional Considerations Research proposals Pilot studies Manipulation checks Debriefing

Communicating Research to Others After the data have been collected, analyzed, and interpreted, communicate the findings to others Write a report first and then communicate 1. Professional meetings 2. Journal articles

The End