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Chapter 8

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David Nussbaum

Chapter 8: Quasiexperimental and Nonexperimental Designs Quasiexperimental design - sometimes cannot directly manipulate IVs -experimenter can select participants who have a particular characteristic or studies participants who have been exposed to specified events such as trauma -when particular individual characteristics are used for the bases of selecting research participants, experimenter is often interested in studying the effects of these subject variables on a dependent measure -Ie. Subject variable = gender is treated as a type of IV -natural treatment = when exposures to events and situations define how participants are selected -exposure and nonexposure as two levels of the IV -subject variables and natural treatments belong to a distinct class of IVs termed ―quasi-independent‖ -quasiexperiment: one that investigates the effects of quasi-independent variable on a dependent variable -‖quasi‖ = ―as if‖ or ―to a degree‖ -resembles true experiment except for the degree to which an experimenter can directly control and manipulate one of more of the IVs -true experiment would be first option but some experiments such as child abuse where can't randomly assign participants to victimized/non victimized groups -quasi experiments offer a fertile research design for investigating some of the most important and creative questions in psychology Two major types of quasi experimental designs: 1. Nonequivalent-control group designs -have experimental and comparison groups that are designated before the treatment occurs and are not created by random assignment 2. Before and after designs -have a pretest and posttest but no comparison group -participants exposed to the treatment serve as their own controls Natural Treatments as Quasi Independent Variables Ie. If we wanted to study psychological effects of 9/11 -9/11 is the quasi-independent variable b/c we cannot directly control or manipulate via random assignment exposure to 9/11 -it is considered naturall treatment created by various events in the real world over which an experimenter has no control ie. war, assassinations, terrorist attacks,natural disasters, new educational curricula, school closings, changes in rules -these cannot be directly manipulated but researcher can only provide an after the fact or ex post facto analysis Subject Variables as Quasi-Independent Variables -Suppose we wanted to study 9/11 but we are interested in gender differences in response to 9/11 -Two quasi-independent variables: natural treatment –9/11 subject variable –gender Ie. Diagnosis of schizophrenia –quasi independent variable -participants were selected based on the subj var of diagnosis and formed experimental group based on the presence of existing schizophrenia and control group based on the absence of schizophrenia -manipulated within subjects two forms of attention social and non social =this is an example of mixed-factorial design –combines both between and within subjects factors Nonequivalent-Control-Group Designs -if groups formed by random assignment differed on the DV, then such difference would be attributable to treatment or the IV -with quasiexperiments, we know control and experimental groups are not formed by random assignment -groups are selected on the basis of pre-existing immutable subject characteristics or exposure to some kind of natural treatment -control group can never be considered to be equivalent to the experimental group -pre-existing differences cannot be equalized by random assignment compared to true experimental -regression artifact –can occur anytime a pretest measure is used for matching -regression to the mean- may be a confounding factor for interpreting results of studies that match groups on pretest measures -impt to consider whenever random assignment is not or cannot be used Before-and-After Designs -common feature: absence of a comparison group -all cases are exposed to the experimental treatments -basis for comparison is provided by comparing pretreatment to the posttest measures -useful for studies that are experienced by virtually every case in some popn such as total coverage programs -simplest type: fixed-sample panel design –with one pretest and one posttest -interrupted-time-series design- often used in quasiexperimental research to examine observations before and after a naturally occuring treatment -ie. Rob ford supporters before and after crack video -accidental rates over the years some pages omitted -multiple group before-and-after design—several before-and-after comparisons are made involving the same IV and Dvs but with different groups -ie. Phillips' study of effect of TV soap opera suicides on # of actual suicides -researcher had 13 diff before-and-after studies, one for each suicide story -repeated-measures panel designs- multiple pretest and posttest observations of the same group and time series designs -stronger than simple before-and-afer panel designs because they allow the researcher to study process by which an intervention or treatment has an impact over time Quasiexperiment of Memories of 9/11 -functional magnetic resonance imaging- different cognitive tasks will elicit different fmri patterns of brain activation some pages ommitted from book preview -used memory as a within subjects variable with two levels: summer 2001 and september 2001 -all participants received the same word cues, presented one at a time for both conditions -researchers recorded brain activity while participants viewed cue words in both summer 2001 and sept 2001 Ex Post Facto Variables and Comparison Groups -9/11 memories have higher ratings than summer 2001 memories on each of the atttributes and individuals differed in their ratings -HOW? WHY? -researcher examined surveys that all participants had completed -distance/proximity to the WTC on the day of attack influenced memory and brain responses to 9/11 -two groups: those closer –downtown group and those farther away –midtown group -this is an example of researchers creating comparison groups ex post facto, or after the fact, meaning, in this instance, after fmri and word rating data had been collected -creation of new subject variable based on their participants ratings -different from factorial experiment in which groups are formed by random assignment and variables are defined conceptually and operationally a priori Correlatioal Relationships -quasiexperiments lack design featu
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