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    Find the 99% confidence interval for mean difference

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    According to the historical data, the life expectancy in Germany is less than or equal to the life expectancy in the United States. A new study has been made to see whether this has changed. Records of 300 individuals from Germany who died recently are selected at random. The 300 individuals lived an average of 78 years with a standard deviation of 5.2 years. Records of 220individuals from the United States who died recently are selected at random and independently. The 220 individuals lived an average of 76.5 years with a standard deviation of 6.9 years. Assume that the population standard deviations of the life expectancies can be estimated by the sample standard deviations, since the samples that are used to compute them are quite large. Construct a 99% confidence interval for M1-M2 , the difference between the life expectancy M1 in Germany and the life expectancy M2 in the United States. Then complete the table below.
    1. What is the lower limit of the 99% confidence interval?
    2. What is the upper limit of the 99% confidence interval?

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    Answer:

    Pooled variance=(5.2^2+6.9^2)/(300+220-2)=0.1441

    So standard ...

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