Rickets Vitamin D, whether ingested as a dietary supplement or produced naturally when sunlight falls on the skin, is essential for strong, healthy bones. The bone disease rickets was largely eliminated in England during the 1950s, but now there is concern that a generation of children more likely to watch TV or play computer games than spend time outdoors is at increased risk. A recent study of 2700 children randomly selected from all parts of England found 20% of them deficient in vitamin D. a) Find a 98% confidence interval. b) Explain carefully what your interval means. c) Explain what 98% confidence means.
Statistics 350 Fall 2006 Exam 1 Solutions (Answers with Explanations) 1. a. This is an experiment because the migraine patients were randomly divided into groups. b. Yes, the control group is the one in which the patients received no treatment. c. The number of headache days is the response variable since we are measuring the effectiveness of acupuncture and sham acupuncture by the extent to which they reduce the occurrence of migraine headaches. d. The variable “age” would be an example of a(n) confounding (or lurking) variable. The effects attributed to (sham) acupuncture may in fact be due to age in the situation described here. 2. None of these are appropriate because this is a bar