Observational Studies and Experiments Answers

A home-improvement store offers a new brand of lawn food that claims to reduce the number of weeds by 30% over a different brand of lawn food. To test the claim, a homeowner plans to use the new brand of lawn food on half of his lawn and the original brand on the other half. The homeowner will count the number of weeds that appear after a month on each half of the lawn. A neighbor explains that there may be confounding variables, such as shade, that might also explain the relationship.

To increase attendance for a flower show, the organizers have chosen flower shops in the area to offer discount coupons to their customers. Half of the stores receive discount coupons for admission, while the other half of the stores receive two-for-one admission coupons. The organizers then compare the number of each type of coupon redeemed at the show.

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 proposes two methods for collecting data.Method 1: As golfers approach the first tee, give some golfers wrist bracelets with magnets and some golfers wrist bracelets without magnets. During the round of golf, keep track of the length of the golfers’ shots.Method 2: Contact golfers who have purchased wrist bracelets with magnets and ask them to provide information about their shot length.

A researcher conducts an experiment using 10 loads of white shirts with similar stains. The loads are divided, and 5 of the loads are washed with name-brand detergent, while the other 5 are washed with store-brand detergent. Volunteers are asked to assess the cleanliness of the shirts.

An auto-parts store offers a fuel additive that claims to increase a vehicle’s gas mileage. The additive is poured into a vehicle’s gasoline tank after the tank is filled. To measure the claim, the store offers a free bottle of the additive to customers who drive SUV's, who then provide information about their gas mileage on the store website. A customer argues that the type of vehicle could be a confounding variable in this study.