6 HP 350 Lecture Slides Feb 23

6 HP 350 Lecture Slides Feb 23 - Chapter 8 HP 350 Spring...

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1 Chapter 8 HP 350 Spring 2010
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2 Nonrandomized Designs For practical or ethical reasons, randomized experiments are not always possible. Nonrandomized studies are often referred to as Quasi-Experimental Designs. Like randomized experimental designs, these designs have treatment conditions, outcome measures, and sampling units. However, quasi-experimental designs do not randomly allocate sampling units to treatment conditions.
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3 Third Variable Problem In randomized experiments, the process of assigning individuals to treatment and control groups by a random process helps to bolster claim of causality when X and Y covary. However, in nonrandomized experiments, a stronger possibility exists that X and Y covary due to another variable, referred to as the “third variable problem .” This third variable problem is a threat to internal validity for nonrandomized experiments.
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4 Types of Nonrandomized Studies Nonequivalent-Groups Design Time-Series Design Single-Case Experimental Design Cross-Lagged Panel Design Longitudinal Design Cross-Sectional Design
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5 Nonequivalent-Groups Design Program Group NR O X O Control Group NR O O NR   = Not randomized O    = Observation (Pre or Post test) X    = Treatment E.G.  Weight loss study- Allocate overweight children to  nutrition curriculum vs. control based upon existing groups. A between-subjects design with allocation to groups without randomization , i.e., “nonequivalent.”
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6 Time-Series Design Defining feature is the study of some phenomena across time. Data is collected at several time points. Interrupted time-series design suggests an intervention or a naturally occurring situation, i.e., interruption, which separates time into “before” and “after” periods. No explicit control vs. treatment groups , but before period could be viewed as control and after period as treatment . Referred to as “found experiments” since naturally occurring. Diagram for Interrupted Time-Series: O O O O X O O O where O = observation, X = interruption E.G. Study of the murder rate in New Orleans between 2002 and 2008. Hurricane Katrina is the interruption in 2005.
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7 Single-Case Experimental Design Single-Case Experimental Design Also referred to as a Small-N Experimental Research and N-of-1 Experimental Research . Considered a sub-category of interrupted time- series design. Includes the following characteristics: 1. One sampling unit or a few unites are studied. 2. Repeated measures are taken of the unit (a within-subjects design ). 3. Random assignment is rarely used.
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Illustrates a study on the effects of teachers’ attention on study behavior of a single student or single case.
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