HW2 Solutions

5 points for each answer, 40 points total

1. Read Lead exposure linked to bad teeth in children and using the article answer the following questions:
    
   1. How many subjects were in this study's data set.
       
      Answer: 24,901 in the lead study/ cavities study. (19,578 in the lead/vitamin C study)
        
   2. What is the treatment variable in this study?
       
      Answer: Blood lead concentration
        
   3. What is the response variable?
       
      Answer: Number of decayed or missing teeth
        
   4. Is this a designed or observational study? Why?
       
      Answer: Observational. The treatment, blood lead level, was not assigned to subjects by anyone.
        
   5. List 4 confounding factors that were controlled for in this study.
       
      Answer: income, proportion of diet due to carbohydrates, calcium in the diet and number of days since last dental visit.
       
2. What two things must a variable do to be a confounding factor?
    
   Answer: It must correlate with the treatment variable (or differ between treatment groups) and it must effect the response variable.
     
3. Recent studies have demonstrated that shorter people live longer than tall people. (Really)
    
   1. Is this an observational study or a designed experiment? Why?
       
      Answer: Observational. Height is not assigned to the subjects.
        
   2. Shoe size is not potential confounding factor in this study. Why not?
       
      Answer: While shoe size correlates with height it does not satisfy the second criteria for a confounding factor: it does not effect life span.
        

E-mail Mr. Callahan at stat110@edcallahan.com with questions or comments about this web site or about the class itself.