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Vocabulary experimental unit an individual upon which

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Vocabulary: Experimental unit – an individual upon which an experiment is performed Subject – a human experimental unit Treatment – a specific experimental condition applied to the experimental units Statistically significant – a term applied to an observed effect so large that it would rarely occur by chance Block – a group of experimental units that are known, prior to the experiment, to be similar in some way that is expected to systematically affect the response to the treatments Double-blind – neither the subjects nor the observers know which treatments any of the subjects had received in an experiment Key Concepts: Parts of an Experiment: Experimental units – individuals on which experiment is done Subjects – experiment units that are human beings Treatment – specific experimental condition applied to units Factors – the explanatory variables in the experiment Level – the combination of specific values of each of the factors Experimental Design Factors: Control Overall effort to minimize variability in the way the experimental units are obtained and treated Attempts to eliminate the confounding effects of extraneous variables (those not being measured or controlled in the experiment, aka lurking variables) Replication Use enough subjects to reduce chance variation Increases the sensitivity of the experiment to differences between treatments Randomization Rules used to assign the experimental units to the treatments Uses impersonal chance to assign experimental units to treatments Increases chances that there are no systematic differences between treatment groups
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Chapter 5: Producing Data Example 1: Draw a picture detailing the following experiment: A statistics class wants to know the effect of a certain fertilizer on tomato plants. They get 60 plants of the same type. They will have two levels of treatments, 2 and 4 teaspoons of fertilizer. Someone suggests that they should use a control group. The picture should include enough detail for someone unfamiliar with the problem to understand the problem and be able to duplicate the experiment. Example 2: A baby-food producer claims that her product is superior to that of her leading competitor, in that babies gain weight faster with her product. As an experiment, 30 healthy babies are randomly selected. For two months, 15 are fed her product and 15 are feed the competitor’s product. Each baby’s weight gain (in ounces) was recorded. A) How will subjects be assigned to treatments? B) What is the response variable? C) What is the explanatory variable? Example 3: Two toothpastes are being studied for effectiveness in reducing the number of cavities in children. There are 100 children available for the study. A) How do you assign the subjects?
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