Statistics in a Modern World 800
Solutions to Exam 1

1.  
   1. (i) observational study
   2. (i) consumption of carbonated beverages
   3. (iii) incidence of broken bones
   4. (iv) all of the above (the article refers to "active teen-age girls", which suggests that active have been studied separately from inactive, teen-age separately from other ages, girls separately from boys: this is how we control for possible confounding variables)
   5. (iii) more soft drinks may mean less milk
2. (i) invalid: using an ordinary household teaspoon could easily lead to perfectly "reliable" measurements in the sense that one consistently overdoses (if the teaspoon is larger than standard) or consistently underdoses (if the teaspoon is smaller than standard). The problem is that the measurement is inaccurate.
3. (ii) "gays forming domestic partnership" tends not to offend people's religious or moral sensibilities... (Nobody got this wrong!)
4. 1. (ii) an experiment because the treatment of modifying TV habits was imposed by researchers
   2. (i) matched pairs (similar schools)
   3. (iii) third and fourth graders
   4. (ii) response variable
   5. (i) explanatory variable
   6. (iii) continuous measurement variable, because time is involved, and time takes on values over a continuous range
   7. (i) open (The question is certainly open, allowing freedom to respond any amount. Some people thought it was biased, suggesting that the children must have watched some TV. However, children could easily have responded "zero" if this was the case.)
   8. 1. Stanford University/Archives of Pediatrics and Adolescent Medicine
      2. 192 third and fourth grade students
      3. intervention group where screen time was reduced through classroom lessons and parental newsletters vs. control group where no effort was made to reduce exposure
      4. 24-(1/3)(24)=16; 4-(.25)(4)=3
   9. (ii) no since students and parents would be aware of the campaign...
5. (i) volunteer sample
6.  
   1. (ii) experiment
   2. (i) subjects should be blind
   3. (iii) make the assignments at random
7. 1. 1752
   2. (i) sample survey/observational study
   3. (ii) prospective because they were first interviewed about their interest in cigarette ads, then had smoking habits evaluated three years later (In a retrospective study, researchers would have simply asked teenagers to remember how interested they had been in cigarette ads in the past, and at the same time evaluated their smoking habits.)
   4. (ii) when they'd had a favorite cigarette advertisement

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