An Ad for ARCO Graphite Motor Oil Says (Really): "Based

question 8

Multiple Choice

An ad for ARCO graphite motor oil says (really) : "Based on a 95% confidence level, our tests achieved between 1% and 8.7% mileage improvement" as compared with a conventional motor oil. What does the phrase "95% confidence level" mean here?

• A) ARCO graphite beats 95% of conventional motor oils.
• B) The interval from 1% to 8.7% covers 95% of the mileage improvements observed in the tests.
• C) The tests included 95% of all oil brands on the market.
• D) The estimate that mileage improves somewhere between 1% and 8.7% came from a method that would catch the true improvement in 95% of all similar tests.
• E) A mistake has been made, because 95% + 8.7% is more than 100%.

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