PSC41 Chapter 11

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one group, pretest/posttest design
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a researcher recruits one group of participants, measures them on a pretest, exposes them to a treatment, intervention, or change, and then measures them on a posttest
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maturation threat
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a change in behavior that emerges more or less spontaneously over time
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history threats
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result from a historical or external event that affects most members of the treatment group at the same time as the treatment, making it unclear whether the change in the experimental group is caused by the treatment received or by the historical factor
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regression threat
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a statistical concept called regression to the mean: when a performance is extreme at Time 1, the next time that performance is measured (Time 2), it is likely to be less extreme-that is, closer to a typical or average performance
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attrition threat
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becomes a problem for internal validity when attrition is systematic, when only a certain kind of participant drops out
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testing threat
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a specific kind of order effect, refers to a change in the participants as a results of taking a test (dependent measure) more than once
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instrumentation threat
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occurs when a measuring instrument changes over time (instrument decay)
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selection-history threat
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an outside event or factor systemically affects people in the study – but only those at one level of the independent variable
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selection attrition threat
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only one of the experimental groups experiences attrition
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observer bias
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occurs when researchers’ expectation influece their interpretation of the results
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demand characteristics
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are a problem when participants guess what the study is supposed to be about and change their behavior in the expected direction
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double-blind study
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neither the participants nor the researchers who evaluate them now who is in the treatment group and who is in the comparison group
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masked design
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when a double-blind study is not possible, a variation might be an acceptable alternative; in some studies, participants know which group they are in but the observers do not (blind design)
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placebo effect
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occurs when people receive a treatment and really improve – but only because the recipients believe they are receiving a valid treatment
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double-blind placebo control study
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one group receives the real drug or real therapy and the second group receives the placebo drug or placebo therapy. however, neither the people treating the patients nor the patients themselves know whether they are in the real group or the placebo group
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null effect
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when a study finds that the independent variable did not make a difference in the dependent variable
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ceiling effect
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all the scores are squeezed together at the high end
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floor effect
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all the scores are cluster at the low end
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manipulation check
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a separate dependent variable that experiments include in a study, just to make sure the manipulation worked
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noise
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too much unsystematic variability (error variance or unsystematic variance)
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measurement error
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any factor that can inflate or deflate a person’s true score on a dependent measure
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situation noise
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external distractions of any kind – is a third factor that could cause variability within groups and obscure true group differences
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a. attrition
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Dr. Weber conducted a long-term study on friendship. he noticed that the most introverted people dropped out by the third session. therefore, his study might have which of the following internal validity threats? a. attrition b. maturation c. selection d. regression
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d. a testing threat refers to a change in the participants over time; instrumentation threats refer to a change in the measuring instrument over time
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how is the testing threat to internal validity different from an instrumentation threat? a. a testing threat can be prevented with random assignment; an instrumentation threat cannot b. a testing threat applies only to within-groups designs; instrumentation threats are for any design c. a testing threat can be prevented with a double-blind study; instrumentation threats can be prevented with a placebo control d. a testing threat refers to a change in the participants over time; instrumentation threats refer to a change in the measuring instrument over time
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b. when the researcher recruits a sample whose average is extremely low or high at pretest
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a regression threat applies especially: a. when there are two groups in the study: an experimental group and a control group b. when the researcher recruits a sample whose average is extremely low or high at pretest c. in a posttest-only design d. when there is a small sample in the study
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a. the dogs loved both treats (her reward manipulation has a ceiling effect)
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Dr. Banks tests to see how many training sessions it takes for dogs to learn to sit and stay. she randomly assigns 60 dogs to two reward conditions: one in which the reward is miniature hot dogs, and one in which the reward is small pieces of steak. surprisingly, she finds that the dogs in each group learn sit and stay in about an equal amount of sessions. given the design of her study, what is the most likely explanation for this null effect? a. the dogs loved both treats (her reward manipulation has a ceiling effect) b. she used too many dogs c. she didn’t use a manipulation check d. there were too many individual differences among the dogs
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a. increased the between-groups variability
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Dr. Banks modifies her design and conducts a second study. she used the same number of dogs and the same design, except now she rewarded one group of dogs with miniature hot dogs and another group of dogs with pieces of apple. she found a big difference, with the mini hot dogs group learning the command faster. Dr. Banks avoided a null result this time because she: a. increased the between-groups variability b. decreased the within-groups variability c. improved the study’s internal validity
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d. power
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when a study has a large number of participants and a small amount of unsystematic variability (low measurement error, low levels of situation noise) then it has a lot of: a. internal validity b. manipulation checks c. dependent variables d. power

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