What extraneous variables could have been problematic in the study of whether using night lights caused nearsightedness?
What will be an ideal response?
In this study, parents with myopia might be more likely to use night lights. Because myopia has a genetic component, the result might have been that people whose children were predisposed to nearsightedness used night lights. The lights may have been irrelevant.
The sample used in the study consisted of children in families who used an eye clinic. It is not clear that the sample was represented of children in general.
The study was retrospective, requiring parents to remember what they had done when their children were infants. This was an average of six years prior to the study, so memories may have been inaccurate.
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