Statistics in a Modern World 800
Solutions to Exam 1

1.  
   1. (i) because premature infants were fed breast milk in the hospital, giving researchers the opportunity to possibly administer the treatment; it would be much less likely that they could control breastfeeding in other infants at home for more than three months
   2. (i)
   3. (i) "better on tests of mental development later in life" suggests a quantitative assessment
   4. (iii)
   5. (ii) (bedwetters or not)
2.  
   1. "2000 students in Winston-Salen and Forsyth County high schools" made up (comprised) the sample. Note: researchers do not "make up" a sample, they take it. Researchers may "make up" a design for producing data, in the sense of inventing a plan, but they do not invent a sample.
   2. (i) The researchers were interested in all teenagers, to compare those who do and do not watch wrestling.
   3. explanatory, explanatory, categorical (two categorical groups were mentioned in paragraph 9: those who watched six or more times and those who didn't watch at all), response
   4. (i) 630=63% of 1000 (ii) 90=9% of 1000
   5. 10+170%(10)=10+17=27
   6. (i) and (ii) (See paragraphs 4 and 12) but not (iii) (See paragraph 13)
   7. (i)
   8. Best answer: Teens who are already prone to violence would tend to be more interested in watching wrestling than non-violent teens. The majority of students answered along these lines.
3.  
   1. (iii) In both studies, researchers took control of the explanatory variable.
   2.  
      1. response (see 5th paragraph)
      2. response (see last paragraph)
      3. explanatory (see 2nd to last paragraph)
      4. explanatory (see paragraphs 3-5)
   3. (i) In principle, the researchers who weighed the filter papers could have been blind to what stage of the stinging process applied. But this may have been difficult to orchestrate, so I also accepted (iv). The researchers in the second experiment could NOT have been blind to whether a stinger had been scraped or yanked from their own skin, nor to the length of time before removal of a stinger.
   4. (i) Stinging paper may be very different from stinging humans.
   5. (i)
   6. (iii) There would be no clear bias in pain reporting, but if many researchers were to report amount of pain, it would be inconsistent; that is, unreliable.
   7. (ii) Experiments are almost never conducted on a random sample of subjects, and we have discussed the fact that this is not a problem, as long as there is a randomized assignment to treatments.
4.  
   1. (v) Since not just one but all of these types of bias are of concern in this situation, I took 2 points off for those who just answered (i) and 3 points off for those who just answered (ii), (iii), or (iv).
   2. 4.4% is stated to be the margin of error. In general, we can be pretty sure that population proportion is within a margin of error of sample proportion (discussed in lecture).
   3. (iv) Sampling frame is the group of individuals from which the sample is actually taken; it is unknown here, as is often the case (discussed in lecture).

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