5 HP 350 Feb. 16 Lecture Slides-instructor

5 HP 350 Feb. 16 Lecture Slides-instructor - Chapter 7...

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1 Chapter 7 HP350 Spring 2010
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2 Why randomized experiments? Randomized experiments help minimize threats to internal validity . Random experiments help bolster claim that X caused Y.
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3 Randomized Experiment Randomized Experiment Participants or groups are randomly assigned to either a treatment group or control group. “Random assignment ” -- each participant has an equal chance or probability of being assigned either group. “Sampling units ” – participants, objects, or groups studied “Treatment ” – manipulation, intervention, or condition to which sampling units are assigned. “Control ” – non-treatment or placebo group.
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4 Random Assignment Why use random assignment in an experiment? Protects against investigators subconscious biases influencing which group receives treatment. Distributes the characteristics of sampling units over experimental and control conditions so as to not bias outcome of study. Permits computation statistics that require the data to have certain characteristics Random assignment in an experiment is accomplished through a set of rules, such as a flip of a coin, or use of random numbers.
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5 True Experiments Randomized experiments are also referred to as a true experimental design. True experimental designs mean that the experimenter has complete control over: who (subjects) what (purpose) when (timing) where (location) and how (procedure)
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6 Experiments Example: A randomized control trial was developed to test the effectiveness of Zoloft in treating depression. Why is it an experiment? IV is manipulated through a treatment (receive high dose of Zoloft) as compared to being measured (measure Zoloft intake). Compare with a control group (which does not receive treatment). Random assignment : Every participant has an equal chance of being assigned to any given group (treatment vs. control).
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7 Independent & Dependent Variables in an Independent & Dependent Variables in an Experiment Experiment In the Zoloft study : Group assignment = IV (or X) The researcher is “manipulating” the Zoloft dosage. Depression = DV (or Y) Presumably changes in depression are due to the effects of the IV (Zoloft) & not characteristics of the participant.
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Procedures for Random Assignment Procedures for Random Assignment Flipping a coin, picking a number Alternate assignment as they come to you. 1 st person= tx group, 2 nd person= control group, 3 rd person= tx group, etc. Use a random numbers table (see P.205). If assign odd number to GROUP A, and even number to GROUP B, with a random number of 10097, we will assign: S 1 A, S 2 B, S 3 B, S 4 A, S 5 A. Note: S
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5 HP 350 Feb. 16 Lecture Slides-instructor - Chapter 7...

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