A manufacturer of novelty items is undecided about the price to charge for a new product. The marketing manager knows that it should sell for about $10 but is unsure of whether sales will vary significantly if it is priced at either $9 or $11. To conduct a pricing experiment, she distributes the new product to a sample of 60 stores belonging to a certain chain of variety stores. These 60 stores are all located in similar neighborhoods. The manager randomly selects 20 stores in which to sell the item at $9, 20 stores to sell it at $10, and the remaining 20 stores to sell it at $11. Sales at the end of the trial period were recorded. What should the manager conclude?