The article "Extravisual Damage Detection? Defining the Standard Normal Tree"(Photogrammetric Engr. and Remote Sensing, 1981: 515–522) discusses the use of color infrared photo graphy in identification of normal trees in Douglas fir stands. Among data reported were summary statistics for green-filter analytic optical densitometric measurements on samples of both healthy and diseased trees. For a sample of 69 healthy trees, the sample mean dye-layer density was 1.028, and the sample standard deviation was .163. a. Calculate a 95% two-sided CI for the true average dye-layer density for all such trees. b. Suppose the investigators had made a rough guess of .16 for the value of s before collecting data. What sample size would be necessary to obtain an interval width of .05 for a confidence level of 95%?

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