Many golfers wear wrist bracelets containing magnets because they claim the magnets improve balance and the length of shots played off the tee. A golfer would like to determine if the claim has merit and plans to collect data on the length of shots played by golfers who use the magnetic bracelets. Another golfer points out that many golfers who purchase the bracelets also purchase other expensive golf equipment, such as golf clubs, and this could be a confounding variable.
Answer
A
Because golfers purchase expensive golf clubs, they may stop wearing their magnetic bracelets, which would interfere with the outcome of the study.
B
Because golfers can be randomly assigned to receive either magnetic bracelets or expensive golf clubs, the expensive golf clubs are a confounding variable.
C
Because golfers using the magnetic bracelets believe they are hitting longer shots, the study may show their shots are not as long as they believe.
D
Because golfers may use both magnetic bracelets and expensive golf clubs, it will be difficult to determine which variable contributes most to longer shots.
Explanation
Expensive golf clubs could also affect shot length. If golfers who wear magnetic bracelets are more likely to use those clubs, the study may not be able to tell whether longer shots are due to the bracelets or the clubs. That makes the clubs a confounding variable, as choice D describes.
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