A market research firm supplies manufacturers with estimates of the retail sales of their products from samples of retail stores.

A market research firm supplies manufacturers with estimates of the retail sales of their products from samples of retail stores. Marketing managers are prone to look at the estimate and ignore sampling error. An SRS of 20 stores this year shows mean sales of 50 units of a small appliance, with a standard deviation of 10.8 units. During the same point in time last year, an SRS of 13 stores had mean sales of 39.092 units, with standard deviation 17.2 units. An increase from 39.092 to 50 is a rise of about 22%