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PSYB01H3 (581)
Chapter 8

Chapter 8

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Connie Boudens

Chapter 8: Quasiexperimental and Nonexperimental Designs QUASIEXPERIMENTAL DESIGN  For independent variables such as age, ethnicity, socio-economic status etc., an
 experimenter either selects participants who have a particular characteristic or studies participants who have been exposed to specified events, such as war or trauma, or might live in certain settings or situations, such as a neighborhood or a geographic region  When particular individual characteristics are used for the bases of selecting research participants, an experimenter is often interested in studying the effects of these subject variables on a dependent measure  When exposures to events, situations, or settings that emanate from the ―real world‖ define how participants are selected, we refer to this type of independent variable as a natural treatment  In studies of the effects of a natural treatment on a dependent variable, exposure and nonexposure would form two levels of the independent variable  Quasiexperiment is one that investigates the effects of a quasi-independent variable on a dependent variable  Quasiexperiment resembles a true experiment except for the degree to which an experimenter can directly control and manipulate one or more of the independent variables o Can randomly assign participants to experimental and control conditions  Quasiexperiments offer a fertile research design for investigating some of the most important and creative questions in psychology  Two major types of quasiexperimental designs o Nonequivalent-control group designs: Nonequivalent-control-group designs have experimental and comparison groups that are designated before the treatment occurs and are not created by random assignment o Before-and-after designs: Before-and-after designs have a pretest and posttest but no comparison group. In other words, the participants exposed to the treatment serve, at an earlier time, as their own controls. NATURAL TREATMENTS AS QUASI-INDEPENDENT VARIABLES  Examples of natural treatments are historical events such as war, presidential assassinations, and terrorist attacks; natural disasters such as hurricanes, earthquakes, and tsunamis; and more ordinary, system-level practices and policies such as new educational curricula, school closings, and changes in rules governing drug prescriptions of physicians  Natural treatments fall into the class of quasi-independent variables that cannot be directly manipulated; the researcher can provide only an ―after-the-fact‖ or ex post facto analysis }f its effect on a particular dependent variable such as memory, suicide rates, or grades SUBJECT VARIABLES AS QUASI-INDEPENDENT VARIABLES  Example: Compared social attention and nonsocial attention as measured by speeded target detection in persons with schizophrenia and in a control group of healthy volunteers o Diagnosis of schizophrenia was the quasi-independent variable: We selected participants on the subject variable of diagnosis and formed our experimental group based on the presence of existing schizophrenia and our control group based on the absence of schizophrenia o Manipulated within subjects two forms of attention, social and nonsocial, and presented these two experimental tasks in a counterbalanced order  Schizophrenia study is an example of a quasiexperiment that used a mixedfactorial design o Combines both between- and within-subjects factors  Presence or absence of a diagnosis of schizophrenia is the between-subjects factor that is used to form patient and control groups o Cannot be manipulated or controlled of the experimenter  Type of attention, social or nonsocial, is the within-subjects factor that is manipulated and under the complete control of the experimenter NONEQUIVALENT-CONTROL-GROUP DESIGNS  Control group can never be considered to be equivalent to the experimental group o Pre-existing differences cannot be equalized by random assignment as would be the case in a true experiment o Most common The
 which is referred to as a nonequivalent-control-group design  Nonequivalent-control-group designs have experimental and control groups that have been predetermined or predesignated by either an existing subject characteristic or an already-occurred natural treatment and are not created by random assignment  Ruth Wageman- used a quasiexperimental design to investigate how the organization of work tasks and rewards affected work team functioning  Research question was whether it was preferable to organize work and work rewards in a way that stressed either interdependence or individual autonomy  Allowed district managers to choose which intervention they would implement in their work team o Management of some teams stressed interdependence, others, autonomy, and still others, a hybrid model in which members worked part of the time as an interdependent team and part of the time as autonomous individuals  Did not use random assignment to determine which team received which management style  She did compare pretest and posttest team performance, her three groups likely differed considerably regardless of whether their district managers stressed interdependence, individual autonomy, or a combination of the two  May be important interactions among the characteristics of the managers and the intervention they chose to apply to their work teams o Ex. Hybrid model may be effective with a certain management personality  Team performance improved more for the hybrid model of management than with either interdependence or autonomy  Quasiexperimental studies with nonequivalent control or comparison groups often receive high marks for their external validity in general, and their ecological validity in particular MATCHING  Individual matching individual cases in the treatment group are matched with similar individuals in the control group o Can create a control group that is very similar to the experimental group  Aggregate matching identifying a comparison group that matches the treatment group in the aggregate rather than trying to match individual cases o Finding a comparison group that has similar distributions on key variables  Researcher matches on a variable that is highly related to the dependent variable  Can collect pretest measures and then match participants either individually or in the aggregate on pretest scores  Regression artifact-threat to internal validity that occurs when subjects who are chosen for a study because of their extreme scores on the dependent variable become less extreme on the posttest due to natural cyclical or episodic change in the variable  Regression to the mean Trend for extreme scores on a measure to move closer to the group average when retested due to inherent unreliability of measurement BEFORE-AND-AFTER DESIGNS  Common feature of before-and-after designs is the absence of a comparison group  Basis for comparison is provided by comparing the pretreatment to the posttest measures  Useful for studies of interventions that are experienced by virtually every case in some population, such as total coverage programs like Social Security  Interrupted-time-series design is often used in quasiexperimental research to examine observations before and after a naturally occurring treatment  John Gibbons and colleagues- interrupted-time-series design to examine the effects of a naturally occurring treatment  Researchers investigated the effect of public health warnings about the safety of antidepressant drugs issued by U.S. and European regulators in 2003 and 2004  Researchers wanted to know whether the policies that discouraged the use of antidepressants in treating children and adolescents had inadvertently led to untreated depression in the young that in turn contributed to their jump in suicide rates  Naturally occurring treatment is the policy change discouraging the use of antidepressants in children and adolescents  Compared suicide rates of children and adolescents before and after the regulators issued their warnings  Gibbons and colleagues interpreted these findings as showing that regulatory policies discouraging the use of antidepressants in children and adolescents may have inadvertently increased suicide rates for these groups  Results have remarkable ecological validity as they suggested antidepressants may help reduce suicide rates of children, adolescent, and adults across counties and states  Studies may De viewed as quasiexperiments of the effects of a natural treatment (public health warnings)on a dependent variable or outcome measure (suicide rates)  David P. Phillips- study of the effect of TV soap-opera suicides on the number of actual suicides in the United States illustrates a powerful 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 Identified 13 soap-opera suicides in 1977 and then recorded the U.S. suicide rate in the weeks prior to and following each TV story o Researcher had 13 different before-and-after studies, one for each suicide story. In 2 of these 13 comparisons, deaths due to suicide increased from the week before each soap-opera suicide to the week after  Repeated-measures panel designs include several pretest and posttest observations, and time series designs, such as the interrupted-time-series study of Gibbons and colleagues, which include many observations in both pretest and posttest periods  Repeated-measures panel designs are stronger than simple before-and-after panel designs because they allow the researcher to study the process by which an intervention or treatment has an impact over time  Time series design - compare the trend in the dependent variable up to the date of the intervention or event whose effect is being studied and the trend in the dependent variable after the intervention  Substantial disparity between the preintervention trend and the postintervention trend is evidence that the intervention or event had an impact  Time series designs are particularly useful for studies of the impact of new laws or social programs that affect everyone and that are readily assessed by some ongoing measurement A QUASIEXPERIMENT
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