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Chapter 8

Chapter 8 Notes 97-03.doc

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David Nussbaum

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PSYB01 Chapter 8 – Quasiexperimental and Nonexperimental Designs Quasiexperimental Design - In many instances, we cannot directly manipulate an independent variable: gender, race, age, ethnicity, SE, locale, diagnosis, personality traits, and personal history are just some examples - For these kinds of variables: experimenters must select participants that have a certain characteristic or those who have been exposed to specified events - Subject variables: The above listed treated as an independent variable - Natural treatment: Naturally occurring event treated as a quasi-independent variable which can be measured but not manipulated (levels may be exposure or nonexposure) - Quasiexperiment: investigates effects of a quasi-independent variable on a dependent variable (quasi meaning “as if” or “to a degree”) - True experiments would be first option but ethically and practically, quasiexperiments are needed - 2 types of quasiexperimental designs o Nonequivalent-control-group-designs: have experimental and comparison groups designated before treatment occurs and are not created by random assignment o Before-and-after designs: pretest and posttest but no comparison group, they are their own controls - Natural Treatments as Quasi-Independent Variables o Example would be 9/11, considered a natural treatment because it is a real world event that experiments have no control over o Some natural treatments may be: war, presidential assassinations and terrorist attacks, natural disasters, ordinary system-level practices and policies such as new educational curricula, school closings, changes in rules governing drug prescriptions, etc. o Ex post facto: “after the fact” analysis, and its effect on a particular dependent variable such as memory, suicide rates or grades - Subject Variables as Quasi-Independent Variables o Mixed factorial designs: combines both between- and within- subjects factors - Nonequivalent-Control-Group Designs PSYB01 Chapter 8 – Quasiexperimental and Nonexperimental Designs o Control groups can never be considered equivalent to experimental group o Have experimental and control groups that have been predetermined or predesignated by either an existing subject characteristic or an already- occurred natural treatment o Ruth Wageman (1995): used quasiexperimental design to investigate organization of work tasks and rewards (interdependence, autonomy or both) o Often high in external validity and ecological validity (high in generalizability and high in realism) - Matching o Individual matching: individual cases in treatment group are matched with similar individuals in control group o Aggregate matching: finding comparison group that has similar distribution on key variables: same average age, same percentage female, etc. o Problems with matching  Regression artifact: threat to internal validity, when subjects are chosen for a study because of extreme scores that become less extreme on posttest due to natural cyclical or episodic change in variable  Regression to the mean: Trend for extreme score son a measure to move closer to group average when retested (unreliable) - Before-and-After Designs o Absence of comparison group o Simplest type is fixed-sample panel design: one pretest and one posttest o Interrupted-time-series design: single experimental group for which we’ve obtained multiple observations before and after a naturally occurring treatment (e.g. comparing accidents before and after a new law goes into effect) o E.g. Study by John Gibbons (2007): discouraging use of antidepressants for children, coincided with large jump in adolescent suicide rates PSYB01 Chapter 8 – Quasiexperimental and Nonexperimental Designs o David P. Philips (1982): study of effect of TV soap-opera suicides on number of actual suicides: illustrates multiple group before-and-after design o Multiple pretest and posttest observations of the same group  Repeated-measures panel design (several pretest and posttest observations) • Repeated measures panel design are stronger than simple before-and-after because they allow researcher to study process over time  Time series designs (many (30+) observations in both pre- and posttest periods) • Useful for studies of impact of new laws or social programs • E.g. Oklahoma City terrorist bombing compared with divorce rate Quasiexperiment of Memories of 9/11 - Functional Magnetic Resonance Imaging (fMRI) – used technique that records brain at work in real time, while an individual works o Uses blood oxygen dependent level (BOLD) signal to measure brain activation o By examining patterns, researchers can identify various neural networks that underlie different kinds of performance such as memory, attention, perception and others - Experimental Stimuli and Task o Word Cues used as Experimental Stimuli in Sharot et al. study (2007) o Distinctive attributes of memories  Arousal, vividness, reliving, remember/know, confidence and valence - Ex Post Facto Variables and Comparison Groups o Those close to WTC and those that weren’t (categorized by 2.08 miles, downtown or midtown) PSYB01 Chapter 8 – Quasiexperimental and Nonexperimental Designs o Very different from factorial experiments where groups are formed by random assignment and variables are defined conceptually and operationally a priori - Correlational Relationships o Correlation Coeffcient: vary from -1.00 to +1.00, numbe
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