Question

Xavier is testing different types of planting soil to determine which type is most effective in growing blueberry bushes. He purchases two different brands of planting soil from a local store. Xavier applies Brand A to an area of the yard that receives full sunlight and Brand B to another area of the yard that is in partial sunlight. He waters the area with Brand B daily; he waters the area with Brand A every other day. At the end of the study, Xavier concludes Brand A is more effective in growing blueberry bushes. Why is his conclusion not valid?

Answer 1

Answer:

He did not control for lurking variables and their impacts on the results of his experiment. Amount of sunlight and water received are two outside variables(or confounding variables) that may impact the growth of his plants and influence the results. He needs to apply the same amount of sunlight and water to each plant within a different planting soil in order to rule out the influence of those two variables and test the sole effect of the soil brand on the plant growth. Otherwise, it would be hard to determine whether his plant growth was because of the soil brand or the different amounts of sunlight and water received