A chain of convenience stores tested a display for a new snack product by placing the display in four different locations in various stores; at the entrance, in the snack section, by the cash register, and with the soft drinks.

Each display location was utilized in three stores over a one-week test period. Because the 12 stores which used to test the display dier somewhat in overall sales volume, they were divided into three categories.

Within each category, the assignment of stores to display method was random. Units sold are shown in the following table:

Unit Sales, by Location Display

Is it possible to be 99% certain that the display locations' mean sales are not equal? Conduct the appropriate follow-up analysis (Use = 0:01) to establish which means are significantly different. List all necessary assumptions and indicate which might be suspect. Also perform a non-parametric analysis.