Which statement best describes the effect of the confounding variables?
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.
Because of confounding variables, the homeowner
should only put the new lawn food on shady spots and
the original brand on sunny spots.
O Because shade is a primary cause of weed growth,
the brand of lawn food used in shady or sunny spots
will not affect the number of weeds.
O If the half of the lawn with the new lawn food shows
fewer weeds after a month, this will prove the new
lawn food is better at stopping weed growth.
The parts of the lawn that receive the new lawn food
may also get more shade than other parts of the lawn,
and the shade might also cause fewer weeds.