Conducting experiments Chapter 9

Manipulating the independent variable Setting the stage Types of manipulations Straightforward Uses instruction and stimulus presentation Staged Used sometimes to create a psychological state Tries to replicate an experience that may happen in real life Employ a confederate (appears to be another participant but is part of the manipulation)

Manipulating the independent variable Strength of the manipulation To be strong, one should maximize the differences b/w the 2 groups Important in the early stages of research Take into account Likelihood of happening in reality Ethics Cost of the manipulation Resources cost money Salaries for confederates, printing, pens, setting

Measuring the dependent variable Self report measures Behavioral measures Physiological measures

Measuring the dependent variable Sensitivity of the DV Should be able to detect differences b/w groups Ceiling effect Occurs if IV appears to have no effect on the DV only b/c participants quickly reach the maximum performance level Scores for different conditions are close to the maximum score so no significant differences can occur To avoid this: Make the task more difficult. Run a pilot study. Floor effect Occurs if the task is so difficult that the subject cannot perform well When a task is so difficult that the experimental manipulation shows little/no effect. To avoid this: Make the task easier. Run a pilot study

Measuring the dependent variable Multiple measures Measuring more than one IV Helps to know if some IVs affects some measures but not others Remember to counterbalance order of presentation

Additional controls Controlling for participant expectations Demand characteristics Any feature of an experiment that might inform participants of the purpose of the study To control use______________ Placebo groups Led to believe treatment is being given when it is not Tests if treatment is working Ethical implications

Additional controls Controlling for experimenter expectations Experimenter bias – researcher develops expectations of how participants should respond Solutions Be consistent with all participants Run all conditions simultaneously Automate procedures Use “blind” experimenters Single blind: Double blind:

Additional considerations Research proposals Have a literature review Tries to explain why the research is being done and what questions the research is trying to answer Includes plans for analysis Used in grant applications Get input from outside parties Pilot studies Trial runs to see if study will work smoothly

Additional considerations Manipulation check An attempt to directly measure whether the IV manipulation has the intended effect on the participants Useful in the pilot study to see if the right effect is created Also useful in the experimental study Debriefing Experimenters interact with the participant to discuss the ethical and educational implications of the study Experimenters can learn more about what participants were thinking Experimenters ask participants to refrain from discussing details of the study with others (future participants).

Analyzing, interpreting and communicating results Analyses Run the appropriate statistics Professional meetings APA, SFN, SPR Talk to other researchers about the latest research Journal articles Research is subjected to peer review Allows research to be distributed widely Accepts high quality work