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Conducting experiments

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

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Conducting experiments

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  1. Conducting experiments Chapter 9

  2. 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)

  3. 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

  4. Measuring the dependent variable • Self report measures • Behavioral measures • Physiological measures

  5. 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

  6. 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

  7. 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

  8. 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:

  9. 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

  10. 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).

  11. 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

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