Sampling distributions

Practice sheet

Fresh questions from the whole chapter, to do on paper.

To save a PDF, choose “Save as PDF” in the print dialog.

  1. Many random samples of size 161 are taken from the same population. Which quantity changes from sample to sample?
    1. The sample proportion p̂ (a statistic)
    2. The population proportion p (a parameter)
    3. The sample size
  2. Compared with samples of size 73, samples of size 292 give sample means that…
    1. vary less around the population mean
    2. vary more
    3. are more biased
  3. What is the sampling distribution of the sample mean for samples of size 25?
    1. The distribution of x̄ over all possible samples of size 25
    2. The distribution of the 25 values in one sample
    3. The distribution of the population
  4. The population proportion is p = 8/10. Find the standard deviation of p̂ for random samples of size 83.
  5. The population proportion is p = 5/10. What is the mean of the sampling distribution of p̂ for samples of size 351?
  6. The population proportion is p = 1/8. What is the smallest sample size n for which np ≥ 10 and n(1 − p) ≥ 10?
  7. A population has standard deviation σ = 9. Find the SD of the sample mean for samples of size 49.
  8. Samples of size 26 give a certain SD of x̄. By what factor must the sample size be multiplied to halve it?
  9. A population has mean 76 and SD 5. A random sample of 4 has mean 77. Find the z-score of this sample mean.
  10. Household incomes are strongly right-skewed. What is the shape of the sampling distribution of x̄ for random samples of 52 households?
    1. Approximately normal, by the central limit theorem
    2. Right-skewed like the population
    3. Uniform
  11. A population is strongly skewed. Is the sampling distribution of x̄ for samples of size 3 approximately normal?
    1. Not necessarily: n = 3 is too small for the CLT to apply to a strongly skewed population
    2. Yes, sample means are always normal
    3. No, sample means are never normal
  12. Which statement is the central limit theorem, for random samples of size 166?
    1. The distribution of sample means is approximately normal
    2. The data in a large sample are approximately normal
    3. The population becomes normal when n is large