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Experimental Research

Experimental Research. Validity and Confounds. What is it?. Systematic inquiry that is characterized by:

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Experimental Research

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  1. Experimental Research Validity and Confounds

  2. What is it? • Systematic inquiry that is characterized by: • An investigator’s direct manipulation (variation) of some factor or factors (IV or IV’s) thought to be causally related to some outcome or outcomes (DV or DV’s) which are observed as data while holding all other factors constant.

  3. Independent Variable • The independent variable: conditions in the experiment • Different situations (rooms, experiences, etc) • Different instructions • Different tasks • Different treatments • Experimental vs. control groups • Bystander study: Manipulate the number of bystanders

  4. Essential Features of Experiments • Independent Variable • Types? • Control group • Dependent variable

  5. Manipulated vs. Subject Variable • Subject variables are characteristics that you cannot manipulate: gender, choosing subjects with high or low anxiety. • Subject variable studies also called “natural groups studies” • Manipulated variables true experimental designs • Create groups where you place/force subjects to be in one group or another • Create anxiety for ½ of the group. • Limitation with a natural groups study can’t draw causal conclusions because you can’t rule out other possible factors that might be the “true” causal factor. • Example: gender

  6. Extraneous variables vs. Confounds • Extraneous Variable: uncontrolled, unsystematic factors or variance. Can be ANY variable that is related to the IV • Creates “noise” and may affect the outcome variable, just not systematically. • Confounding variable: uncontrolled, systematic variance • Affects the different levels of the IV differently. • 2 things to control for confounds: • Random assignment • Within Subjects designs

  7. Internal vs External Validity • External validity: the extent to which the results of ones study can be generalized to subjects and/or conditions outside of the study. Often done by replication studies • Internal validity: found when results are characterized by the ABSENCE of competing explanations. You are confident that changes in the IV did indeed lead to changes in the DV. • Experimental control is the key to internal validity • An absence of confounds and extraneous variables • Control groups help establish internal validity

  8. Threats to Internal Validity • Post test study • Treatmentobservation • Ritalin and ADHD • Pre test-post test study • Observation treatmentobservation- Offers a baseline measurement from which we can compare

  9. Threats to Internal ValidityIn pre test-post test studies we find.. • History and maturation • History: Something external happens and affects changes in your independent variable • maturation: external to your study, but internal to your subjects. Development or experience • Regression to the mean • When people are chosen because they are ‘extreme’ in some way and you measure their change over time in that extreme dimension • you’re likely to see a change in the score closer to the mean. • Instrumentationand testing • Change in the researchers (or subjects) instrumentation or measuring over time. • Testing: when actually taking the test affects the behavior or helps “practice”. IDU study • Instrumentation: changes in the instrument used to measure from pre to post.

  10. Controlling Against TtIV • Use a Control Group • Observation Treatment Observation AND • Observation---------------- Observation OR • Observation Placebo--- Observation • But, what if these threats don’t affect both groups equally?

  11. Example • Want to know the sexual assault opinions of UWT students • Group 1: Wild life video 2 weeks later… • Group 2: Assault video But during those 2 weeks there was a string of sexual assaults on campus • What kind of threat? • Solution?

  12. Other Threats • Other threats come from HOW a subject is chosen for the study and how comparison groups are formed • Subject selection- if subjects chosen for one group are different than those in another group before the study takes place. • Solution: Random assignment of subjects into groups • Attrition/subject mortality- When subjects drop out or refuse to take part in your experiment. • Possible solution: try to interview the people who dropped out to find out why and see if that is related to the IV

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