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Chapter 1: Q 2. (page 31)
Almost any inferential study involves aspects of descriptive statistics. Explain why.
To organize any summarised information collected from a sample, descriptive statistics are used in inferential studies.
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Medical Testing on Animals. In its Summer 2013 Animal Action Report, the National Anti-Vivisection Society stated that "59% of Americans between the ages of 18 and 29 oppose medical testing on animals." The percentage of 59% was computed from sample data.
(a). Identify the population under consideration.
(b). Identify the sample under consideration.
(c). Is the statement in quotes descriptive or inferential?
(d). If you wanted to make it clear that the percentage of 59% was computed from sample data, how would you rephrase the statement in quotes?
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.
In this section, we discussed two types of statistical designs. Identify and explain the meaning of each one.
The Salk Vaccine. In Exercise 1.17 on page 8, we discussed the Salk vaccine experiment. The experiment utilized a technique called double-blinding because neither the children nor the doctors involved knew which children had been given the vaccine and which had been given placebo. Explain the advantages of using double-blinding in the Salk vaccine experiment.
Dental Hygiene: Which Toothbrush? In an experiment reported by J. Singer and D. Andrade in the article " Regression Models for the Analysis of Pretest / Posttest Data " ( Biometrics, Vol . 53, pp . 729-735 ), the effect of using either a conventional or experimental ( hugger ) toothbrush was investigated. Twelve female and 12 male preschoolers were selected. Within each gender group, six were randomly assigned to the conventional toothbrush and the remaining six to the experimental toothbrush. After each subject brushed with the assigned toothbrush, a dental plaque index was measured. The higher the dental plaque index, the greater was the amount of plaque on an individual's teeth.
(a) Is the statistical design described here a completely randomized design or a randomized block design? Explain your answer.
(b) If the statistical design is a randomized block design, what are the blocks?
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