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designed cofound

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there is an alternative explanation because the experiment was poorly designed; another variable happenedj to vary systematically along with the intended independent variable

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selection effect

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a confound exists because the different independent variable groups have different types of participants.

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order effect (in within group designs)

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there is an alternative explanation because the outcome might be caused by the independent variable, but it also might be caused by the order in which the levels of the variable are presented

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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 overtime

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history threats

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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. *the external factor must affect everyone or almost everyone in the group.

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comparison groups

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help control for history threats and maturation threats

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regression threat

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refers to 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 average performance.

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regression threats

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occur only in a pretest/posttest designs, and only when a group has an extreme score at the pretest. If the group is usually high or low at the pretest, you can expect them to regress toward the mean somewhat when it comes time for the posttest.

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preventing regression threats

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comparison groups can help, along with a careful inspection of the pattern of results.

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attrition

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is a reduction in participant numbers that occurs when people drop before the end.

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attrition

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can help when pretests and post test are administered on separate days, and some participants are not available on the second day.

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attrition threat

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becomes a problem for internal validity when attrition is systematic; that is, 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 result of taking a test more than once. People might have become more practiced at taking the test, leading to improved scores, or they may become more fatigued or bored, which could lead to worse scores over time. (PARTICIPANT CHANGES)

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to avoid testing threats

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researchers might abandoned a pretest all together, or might use alternative forms of the test for the two measurements.

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instrumentation threat

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when a measuring instrument changes over time

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selection history threat

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an outside event or factor systematically affects people in the study - but only those at one of the 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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can be a threat to internal validity in almost any study in which there is a behavioral dependent variable.

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observer bias

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occurs when researchers expectations influence their interpretation of the results

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comparison groups

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can prevent many threats to internal validity, they do not necessarily control for observer bias.

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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 the behavior in the expected direction

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double blind study

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in which neither the participants nor the researchers who evaluate them know who is in the treatment group and who is in the comparison group

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masked design or blind design

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when a double blind study is not possible. in some studies, participants know which group they are in but the observers do not.

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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

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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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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 cluster at the low end

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manipulation check

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is a separate dependent variable that experimenters include in a study, just to make sure the manipulation worked

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noise

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another reason a study might return a null effect is that there is too much unsystematic variability within each group.

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measurement error

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any factor that can inflate or deflate a persons 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 difference

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error variance

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Unsystematic variability in a study is also known a

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to prevent attrition

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Which of the following is NOT a reason a researcher might choose to conduct a double-blind placebo control group study?

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reverse confound

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A confound that keeps a researcher from finding a relationship between two variables is known as a/an:

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null effect

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Imagine that Dr. Bloedorn finds no difference between the calories consumed with the drink additive and without. This is known as:

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a masked design

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When a double-blind study is not possible, an acceptable alternative may be a ________.

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They can be avoided with counterbalancing.

answer

Which of the following is true of instrumentation threats?

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regression

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magine that in Dr. Schulenberg's study, he notes that all of the students do extremely well on the midterm exam. When he looks at the results of the final exam, he notices that all the students' exam scores went down. Given this information, which of the following threats might be present in his study

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it causes more overlap between experimental/comparison groups.

answer

In what way does high within-groups variance obscure between-groups variance?

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a weak manipulation

answer

Dr. Morimoto is curious as to whether exposing people to violent video games causes them to be more aggressive. He assigns half his participants to play a video game for five minutes and the other half to play for seven minutes. He finds that there is no relationship between playing the game longer and being more aggressive. What might be to blame for this null effect?

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because people tend to prefer reading about difference more than similarities

answer

Why is there a publication bias against null effects?

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