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quiz2a_soln - ANS This is a sample survey since a set of...

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MA 2611 B’ 07 Quiz 2a Solution 1. (15 points) Three studies are described below. Tell as precisely as possible what type of study each is. (a) Scientists randomly divide volunteers into two groups. In one group, each individual is given a geometric puzzle to solve, while each individual in the other group is given no stimulation. After five minutes, magnetic resonance imaging (MRI) measurements of the individual’s brain activity are obtained. ANS: This is a controlled experiment since treatments (puzzle or no activity) are assigned to experimental units (subjects) in order to observe a response (MRI measurements). (b) Crop yields are estimated by satellite. First the US is divided into sectors that can be viewed by the satellite in a single image. Images are obtained of a set of sectors selected by a probability sampling scheme. These images are analyzed to estimate the total US crop yield.
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Unformatted text preview: ANS: This is a sample survey since a set of sampling units (sectors) is selected from the population of sectors to obtain information about that population. (c) In order to identify possible causes of tread separation on a particular model of SUV tire, quality engineers compare a sample of failed tires with a sample of unfailed tires with respect to a number of variables. ANS: This is a case-referent (or retrospective) observational study , since tires are grouped by end result (failure or not) and differences in hypothesized causes sought. 2. (5 points) Explain the best way to use blocking to improve the study described in 1(a). Be sure to tell how the blocking would help. ANS: Use each subject as a block and measure each under treatment (puzzle) and control (no stimulation). This would help reduce subject to subject variation....
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