答案和详解如下： Q1. Which of the following statements about sampling and estimation is most accurate? A) A point estimate is a single estimate of an unknown population parameter calculated as a sample mean. B) A confidence interval estimate consists of a range of values that bracket the parameter with a specified level of probability, 1 − β. C) Time-series data are observations over individual units at a point in time. Correct answer is A) Time-series data are observations taken at specific and equally-spaced points.
A confidence interval estimate consists of a range of values that bracket the parameter with a specified level of probability, 1 − α. Q2. Which of the following statements about sampling and estimation is most accurate? A) The standard error of the sample means when the standard deviation of the population is unknown equals s / √n, where s = sample standard deviation. B) The probability that a parameter lies within a range of estimated values is given by α. C) The standard error of the sample means when the standard deviation of the population is known equals σ / √n, where σ = sample standard deviation adjusted by n − 1. Correct answer is A) The probability that a parameter lies within a range of estimated values is given by 1 − σ. The standard error of the sample means when the standard deviation of the population is known equals σ / √n, where σ = population standard deviation. Q3. A range of estimated values within which the actual value of a population parameter will lie with a given probability of 1 − α is a(n): A) (1 − α) percent confidence interval. B) α percent confidence interval. C) α percent point estimate. Correct answer is A) A 95% confidence interval for the population mean (α = 5% is the p-value), for example, is a range of estimates within which the actual value of the population mean will lie with a probability of 95%. Point estimates, on the other hand, are single (sample) values used to estimate population parameters. There is no such thing as a α percent point estimate or a (1 − α) percent cross-sectional point estimate. Q4. Which of the following characterizes the typical construction of a confidence interval correctly? A) Standard error +/- (Point estimate / Reliability factor). B) Point estimate +/- (Reliability factor x Standard error). C) Point estimate +/- (Standard error / Reliability factor). Correct answer is B) We can construct a confidence interval by adding and subtracting some amount from the point estimate. In general, confidence intervals have the following form: Point estimate +/- Reliability factor x Standard error Point estimate = the value of a sample statistic of the population parameter
Reliability factor = a number that depends on the sampling distribution of the point estimate and the probability the point estimate falls in the confidence interval (1 – α)
Standard error = the standard error of the point estimate | 
发表于 2009-4-10 15:04
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