Data scientists conducted a study of 15,000 people living in Alaska and New Mexico. They wanted to find out if people in colder climates spent more money on footwear. They discovered that Alaskans spent an average of $150 per year on shoes, whereas New Mexicans spent an average of $45 per year.
Before publishing their findings, the data scientists have asked you to review their claim. In the space below, indicate possible threats to validity faced by this study.
These materials were developed partly through support of the National Science Foundation,
(awards 1042210, 1535276, 1648684, and 1738598). 
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