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Chapter 1: Q 1.6. (page 7)
Fill in the following blank:
Observational studies can reveal only association, whereas experiments can help establish .
Observational studies can reveal only association, whereas experiments can help establish causation.
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In sampling, explain why obtaining a representative sample is important.
In Exercises 1.17-1.22, state whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.
Heart Failure. In the paper "Cardiac-Resynchronization Therapy with or without an Implantable Defibrillator in Advanced Chronic Heart Failure" (New England Journal of Medicine, Vol. 350, pp. 2140-2150), M. Bristow et al. reported the results of a study of methods for treating patients who had advanced heart failure due to ischemic or nonischemic cardiomyopathies. A total of 1520 patients were randomly assigned in a 1:2:2 ratio to receive optimal pharmacologic therapy alone or in combination with either a pacemaker or a pacemaker-defibrillator combination. The patients were then observed until they died or were hospitalized for any cause.
Lifetimes of Flashlight Batteries.Two different options are under consideration for comparing the lifetimes of four brands of flashlight battery, using 20 flashlights.
(a) One option is to randomly divide 20 flashlights into four groups of 5 flashlights each and then randomly assign each group to use a different brand of battery. Would this statistical design be a completely randomized design or a randomized block design? Explain your answer.
(b) Another option is to use 20 flashlights - five different brands of 4 flashlights-each and randomly assign the 4 flashlights of each sign be a completely randomized design or a randomized block design? Explain your answer.
Regarding probability sampling:
(a) What is it?
(b) Does probability sampling always yield a representative sample?
(c) Identify some advantages of probability sampling.
Plant Density and Tomato Yield. In "Effects of Plant Density on Tomato Yields in Western Nigeria" (Experimental Agriculture,Vol. 12(1), pp. 43-47 ), B. Adelana reported on the effect of tomato variety and planting density on yield. Four tomato varieties (Harvester, Pusa Early Dwarf, Ife No. 1, and Ibadan Local ) were grown at four densities ( 10,000, 20,000, 30,000, and 40,000 plants/ha). Identify the
a. experimental units. b. response variable.
c. factor (s). d. levels of each factor.
e. treatments.
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