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Chapter

Chapter 5 - Introduction to Experimental Research (DETAILED NOTES)

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Department
Psychology
Course
PSYC 2030
Professor
Rebecca Jubis
Semester
Winter

Description
Chapter 5 - Introduction to Experimental Research All research methods have advantages and disadvantages. The method of choice depends on what you want to find. Advantages of the experimental method: Uses random assignment which allows you to infer cause and effect. Control vs. experimental group. Vary one or more variables while holding others constant. Disadvantages: Generalizability. Lab versus field research. Most experimental research is done in the lab and most of the time this research is not realistic. 2 types of variables: Variable: anything that can be changed. Comes from the word vary. You have to have at least one IV and one DV. In some cases, there can be more than one. Independent variable (IV): this is what the experiment manipulates or varies to see if it has an effect on a given behaviour. (CAUSE) Dependant variable (DV): this is the behaviour that is measured to see if the IV has an effect. (EFFECT) Example: To see if alcohol impairs memory. IV: alcohol. 0oz, 2oz and 4oz (3 levels=conditions=groups) DV: memory DV is dependent on the IV. Memory scores depend on how much alcohol is consumed. If it is not mentioned then it is not an IV and/or DV. Extraneous variable: variables that are not controlled and are of no interest to the experiment. They are not problematic as long as they are held constant. For example: every subject is exposed to it. Assumption that there are an equal number of subjects in all groups (random assignment). An extraneous variable becomes a problem when it is not held constant. Confounding variable: also known as a “uncontrolled extraneous variable”. A variable that you do not want. Example: study time vs. grade. 0hrs, 61%; 5hrs, 73%; 10hrs, 61%. Now what if the 10 hour group did not get any sleep? Then sleep is a confounding variable. A confounding variable changes with the independent variable. It can also affect the dependant variable. To eliminate a confounding variable you can change it into an independent variable. You do this by having half sleep and the other half not sleep. Control Group: must have in an experiment. The group that gets the 0 level of the I.V. The treatment is withheld. Used as the basis for comparison. Any other group besides the control group is called an experimental group. All groups must be equal in every way except for the IV. On average these groups are equal to each other. I.V can be a manipulated variable or subject variable. Manipulated variable: the experimenter creates the situations that the subjects will encounter. Subject variable: refers to already existing characteristics of subjects. Something that you cannot take away from the subject. Is it possible to randomly assign subjects into groups that are created? (To differentiate between manipulated and subject variables) Example: age is selected not assigned. It is not possible to have a real control group. 2 things: no random assignment and you have to select your subjects. YOU CANNOT INFER CAUSE AND EFFECT with subject variables. Quasi-experiments. All you can say is that the groups performed differently. With a manipulative variable, you can infer cause and effect. VALIDITY: (in an experiment)
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