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PSYB01H3 (581)
Chapter 8

Chapter 8

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Department
Psychology
Course
PSYB01H3
Professor
David Nussbaum
Semester
Fall

Description
Chapter 8: Quasi Experimental and Non-experimental Designs  Randomization is what make experiments true Quasi Experimental Design  When we cannot directly manipulate an independent variable  Subject variables: type of an independent variable; particular individual characteristics that cannot be manipulated and instead must be selected; ex. Gender, history, traits, locale etc  Natural treatment: when exposures to events situations or setting that emanate from the real world define how participants are selected; levels are exposure and non exposure; ex historical events, natural disasters, policy changes  Quasi experiment: one that investigates the effects of a quasi-independent variable on a dependent variable o Nonequivalent-control-group design: have experimental and comparison groups that are designated before the treatment occurs and are not created by random assignment o Before and After Designs: have a pre-test and a post test but no comparison groups participants; the participants exposed to the treatment were at an earlier time their own controls  Other quasiexperimental designs similar to this: interrupted-time-series design, multiple-group before-and-after design, repeated-measures-panel designs o There are more kinds as well Natural Treatments as Quasi-Independent Variables o Ex post facto: analysis, after the fact analysis of its affect on particular dependent variable Subject Variables as Quasi-Independent Variables o Can combine quasi-independent variables and manipulated independent variables o Mixed factorial design: combines both between- and within-subjects factors Nonequivalent-Control-Group Designs o As its not random assignment control group cannot be considered equivalent to experimental group o Have high external validity and ecological validity in particular Matching o Individual matching: individuals in treatment group are matched with similar individuals in the control groups o Aggregate matching: identifying a comparison group that matches the treatment group in the aggregate o NOTE: individuals must not be able to choose which group they are in o Regression artifact: statistical phenomenon that can occur anytime a pretest measure is used  Regression to the mean: when compare groups regardless of any kind of intervention people who received extreme scores on a test of ability when retested on that same ability earn scores that are closer to the mean of their group than were their original scores  Confounding factor for interpreting results of studies that match groups on pretest measures Before-and-After Designs o Useful for studies of interventions that are experienced by every case in the population o Fixed-sample panel design: simplest; see Chapter 5 o Interrupted-time-series design: single experimental group for which multiple observations are taken before and after a naturally occurring treatment ex. Public policy change  Have to know when time series is interrupted by natural occurring treatment  Ex. Suicide rates and discouraging use of antidepressants o Multiple group before-and-after design: several before and after comparisons are made involving the same independent and dependent variables but with different groups o Repeated-measures panel designs: involves multiple pretest and posttest observations of the same group; allow study of impact over time o Time-series design: involve many observations in both pretest and posttest periods; disparity between preintervention trend and postintervention trend is evidence that intervention had an impact; useful in studying new laws or social programs A Quasiexperiment of Memories of 9/11 o Functional magnetic resonance imaging (fMRI): uses blood oxygen dependent level signal (BOLD) signal to measure brain activation while participants perform various tasks Experimental Stimuli and Task o Experimental stimuli were word cues ex. Morning, New York City, lunch, evening , weather; recorded brain response to these words and then rated each word on arousal, vividness, reliving, remember/know, confidence and valence o Two experimental conditions: September 2001 and summer 2001 and same words in each condition Ex Post Facto Variables and Comparison Groups o Created comparison groups of distance away from towers ex post facto to account for differences seen in ratings of memories o Recollective experience enhancement: a new subject variable from the combination of the 6 characteristics Correlational Relationships o Has low internal validity lessening confidence in causal conclusions o Correlation coefficient: statistic that tells the degree and direction of a relationship between two variables o Scatter diagrams: graph of a correlation involving two variables o Amygdala: almond shaped structure deep in the brain that plays a key role in fusing memories
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