Question 6.46

6.46 Confidence intervals for average annual income.

Based on a 2012 survey, the National Statistics Office of the Republic of the Philippines released a report on various estimates related to family income and expenditures in Philippine pesos. With respect to annual family income, we would find the following reported:14

Estimate Standard
error		 Lower Upper
Average annual
income		 234,615 3,235 ? 240,958

The “Lower” and “Upper” headers signify lower and upper confidence interval limits. As will be noted in Chapter 7, the “standard error” for estimating the mean is . But because the sample sizes of the national survey are large, is approximately equal to the population standard deviation.

  1. What is the value of the lower confidence limit?
  2. What is the value of the margin of error?
  3. Determine the level of confidence used.

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