Question

I promise a FAN AND A MEDAL!!!!!!

Sarah is testing different types of planting soil to determine which type is most effective in growing blueberry bushes. She purchases two different brands of planting soil from a local store. Sarah applies Brand A to 1 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, Sarah concludes Brand B is more effective in growing blueberry bushes. Why is her conclusion not valid,

Answer 1

Sarah's conclusion is invalid, because she is testing two variables at once without a control value. In order for the experiment to be valid, Sarah should either apply the same soil to both areas (assuming they are, in fact, the same). Or, she should water both equally. At this time, we don't know if B grew "better" due to the brand or the amount of water received.