Stat 10, UCLA
Chapter 6 Solutions
- The tape may have stretched or perhaps moved.
- Yes, as the tape stretches or the cloth moves.
- False: chance errors are sometimes positive, sometimes negative.
Bias pushes one way; if you, for example, consistently sample the
largest rabbits in a population, then you will always over-estimate
the size of the rabbits in the true population.
- False: same reason.
- About 0.03 inches.
- No, the students did not work independently of one another. Students
2 and 10 both got exactly the same answers, and both of these students
recorded their answers to the wrong decimal place (2 places instead of
3). The other students seem fine.
- Tell your friend that these are all measurements on the same thing, and
yet they differ so much from one another. No two people who worked
independently got the same answer!!!
Special Review Exercises
- (600+650)/2 = 625.
- It would be more than 125 because the distributions are different,
so when they are combined there will be more variability.
It would be too low, because the curve is lower than the histogram in that
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
- If the drivers were older, they might just have higher rates heart
disease because of age. (Older people have higher rates of heart
- Any effects of exercise might take a while to show up.
- Drivers are more likely to be similar to conductors with respect
to age, education,
income, socioeconomic background, ethnicity, etc.
- This is an observational study and there are several plausible
For example, drivers might have been heavier to begin with.
- 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.