Nearsightedness Study Myopia, or nearsightedness, results from a number of genetic and environmental factors. In 1999, Quinn et al studied the relation between myopia and ambient lighting at night (for example, from nightlights or room lights) during childhood.
Question 1. The data were gathered by the following procedure, reported in the study. "Between January and June 1998, parents of children aged 2-16 years [...] that were seen as outpatients in a university pediatric ophthalmology clinic completed a questionnaire on the child's light exposure both at present and before the age of 2 years." Was this study observational, or was it a controlled experiment? Explain.
Question 2. The study found that of the children who slept with a room light on before the age of 2, 55% were myopic. Of the children who slept with a night light on before the age of 2, 34% were myopic. Of the children who slept in the dark before the age of 2, 10% were myopic. The study concluded that, "The prevalence of myopia [...] during childhood was strongly associated with ambient light exposure during sleep at night in the first two years after birth."
Do the data support this statement? You may interpret "strongly" in any reasonable qualitative way.
Question 3. On May 13, 1999, CNN reported the results of this study under the headline, "Night light may lead to nearsightedness." Does the conclusion of the study claim that night light causes nearsightedness?
Question 4. The final paragraph of the CNN report said that "several eye specialists" had pointed out that the study should have accounted for heredity.
Myopia is passed down from parents to children. It's also reasonable to suppose that myopic parents are more likely to leave lights on in their children's rooms than other parents. In what way does the knowledge of this possible genetic link affect how we consider the data?
7. Studying the Survivors
The Reverend Henry Whitehead was skeptical of John Snow's conclusion about the Broad Street pump. After the Broad Street cholera epidemic ended, Whitehead set about trying to prove Snow wrong. (The history of the event is detailed here.)
He realized that Snow had focused his analysis almost entirely on those who had died. Whitehead, therefore, investigated the drinking habits of people in the Broad Street area who had not died in the outbreak.
What is the main reason it was important to study this group?
1) If Whitehead had found that many people had drunk water from the Broad Street pump and not caught cholera, that would have been
evidence against Snow's hypothesis.
2) Survivors could provide additional information about what else could have caused the cholera, potentially unearthing another cause.
3) Through considering the survivors, Whitehead could have identified a cure for cholera.
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Note: Whitehead ended up finding further proof that the Broad Street pump played the central role in spreading the disease to the people who lived near it. Eventually, he became one of Snow's greatest defenders.