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Lecture10S - ±.4 t.025 is about 2 for most df(see Table 4...

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Statistics 371-001, Sp 09 Lecture #10 19 Feb 09 Example 6.9 uses 80 df to find the t-value in Table 4. n = 94, df = 93. 93 is not in Table 4. df = 100 is nearer to 93 than 80. 80 df gives a wider confidence interval than 100 df. Is more conservative; more likely to contain the mean. 6.4 Planning a Study – determining n SE = In soybean plant study, SE = .34 cm Want SE ≤ .2 cm – why? Want to be ± .4 cm of population mean for 95% of possible samples of given size. ± t .025 want
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Unformatted text preview: ± .4 t .025 is about 2 for most df (see Table 4), is SE 2 times ??? = .4, 2 times 0.2 = .4 s best estimate is from earlier study, 1.22 cm. ≤ 0.2 , ≤ 0.2 , n = 37.2 38 plants 6.5 Validity of Estimation Methods 1. Conditions of study design – the brood/bird homework problem. Random sample of population – not biased. Independent observations. 2. Conditions for validity of confidence interval. Normal shape/sample size (Section 5.4)....
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