1 Average sale, calculated on a total company basis, is defined as the average invoiced sale per customer, measured on a monthly basis and excluding transactions of less than $250 (which are generally sample orders, or add-ons or fill-ins to previous orders) and of more than $30,000 (which are usually contractor orders) 2 Average retail price per unit sold is calculated on a total company basis and excludes certain service revenue, which consists primarily of freight charges for in-home delivery 3A store is generally considered comparable on the first day of the thirteenth full calendar month after opening 4Approximated by applying our average sale to total net sales at comparable stores

The significant drivers of gross margin expansion and their estimated impact compared to the prior quarter and the prior year are as follows:
    Three Months Ended   Year Ended
December 31, December 31,
Driver Description 2012   2011 2012   2011
  (in basis points)

expansion (contraction)
     
Cost of Product Cost of acquiring the products we sell from our suppliers, including the impact of our sourcing initiatives; Changes in the mix of products sold; Changes in the average retail price per unit sold. 220 260 200 140
 
Transportation International and domestic transportation costs, including the impact of international container rates; Customs and duty charges; Fuel and fuel surcharges; Impact of mill shipments received directly by our stores; Transportation charges from our distribution centers to our stores; Transportation charges between stores and the cost of delivery to our customers. 20 (80 ) 40 (60 )
 
All Other Investments in our quality control procedures; Warranty costs; Changes in finishing costs to produce a unit of our proprietary brands; Inventory shrink; Net costs of producing samples.   120     (30 )   30     (30 )
 
Total Change in Gross Margin from the prior year   360    

150
    270     50  
 

The following table sets forth components of SG&A expenses for the periods indicated, as a percentage of net sales.
   
Three Months Ended Year Ended
December 31, December 31,
2012   2011 2012   2011
Total SG&A expenses 27.4 % 27.7 % 28.3 % 29.1 %
Salaries, Commissions and Benefits 11.9 % 12.2 % 12.1 % 11.8 %
Advertising 6.4 % 6.2 % 7.2 % 7.7 %
Occupancy 3.8 % 4.1 % 3.8 % 4.0 %
Depreciation and Amortization 1.2 % 1.2 % 1.2 % 1.2 %
Stock-based Compensation 0.5 % 0.6 % 0.5 % 0.6 %
Other SG&A Expenses 3.7 % 3.5 % 3.5 % 3.8 %

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