Stat 1040
Chapter 6 Solutions

  1. About 0.03 inches.

Special Review Exercises

S6.
  1. (600+650)/2 = 625.
  2. It would be more than 125 because the distributions are different, so when they are combined there will be more variability.

S8.
It would be too low, because the curve is lower than the histogram in that range.

S10.
False. The data are cross-sectional. One possible explanation is that when those 70 year olds were young, people were forced to write with their right hand, now they are not. To decide what happens to people as they age, you need a longitudinal study.

S13.
  1. If the drivers were older, they might just have higher rates heart disease because of age. (Older people have higher rates of heart disease).
  2. Any effects of exercise might take a while to show up.
  3. Drivers are more likely to be similar to conductors with respect to age, education, income, socioeconomic background, ethnicity, etc.
  4. This is an observational study and there are several plausible confounding factors. For example, drivers might have been heavier to begin with.
  5. See if the drivers were heavier (had larger uniforms) than the conductors at the time of hire. If both groups were the same, initial weight is not the confounding factor. If drivers were heavier to begin with, the argument that exercise matters is much weaker. Note: looking at size after 10 years does not help us to decide.