Mina is testing different types of heat lamps to determine which type is most effective for growing strawberry bushes. She purchases two different types of lamps from a local store. Mina applies brand A to one area of the yard and brand B to another area of the yard, both of which receive full sunlight. She waters the area with brand B daily; she waters the area with brand A every other day. At the end of the study, Mina concludes brand B is more effective in growing strawberry bushes. Is Mina's conclusion valid? Explain why or why not.