Parker is testing 2 different types of ant killer in his yard. He purchases Brand A and Brand B from the home improvement store. He applies Brand A in the front yard on Monday and Brand B in the backyard on Saturday. He then compares the ant hills on Sunday and determines that Brand A is more effective than Brand B. Why is his conclusion not valid?
He included another variable - time. He should have given both brands the same amount of time to work. The only variable should have been the brands. Parker has introduced another variable and therefore his results are invalid.
