Larry has purchased a device that the manufacturer claims will reduce the fuel consumption in his car. After a month has passed, Larry determines that his mileage currently rests at 17 miles per gallon. Larry's best friend, Steve, owns the exact same make and model car, and has calculated his mileage at 23 miles per gallon. Steve's car does not have the device that Larry purchased one month ago. Larry then makes the conclusion that the manufacturer of the device's claim is not true.
Which of the following statements would cause Larry's conclusion to be the weakest?