products. Due to the Company’s significant international operations, financial results can be significantly affected by fluctuations in exchange rates. 

The year-over-year growth in 2014 and 2013 R&D expense was driven primarily by an increase in headcount and related expenses, including share-based compensation costs and machinery and equipment to support expanded R&D activities. The Company continues to believe that focused investments in R&D are critical to its future growth and competitive position in the marketplace and are directly related to timely development of new and enhanced products that are central to the Company’s core business strategy. As such, the Company expects to make further investments in R&D to remain competitive. 

Selling, General and Administrative (“SG&A”) Expense 

The growth in SG&A expense during 2014 compared to 2013 was primarily due to increased headcount and related expenses, including share- based compensation costs; higher spending on marketing, advertising and professional services; and the Company’s continued expansion of its Retail segment. The growth in SG&A during 2013 compared to 2012 was primarily due to the Company’s continued expansion of its Retail segment and increased headcount and related expenses, partially offset by decreased spending on professional services. 

The decrease in other income and expense during 2014 compared to 2013 was due primarily to higher interest expense on debt and higher expenses associated with foreign exchange rate movements, partially offset by lower premium expenses on foreign exchange contracts and higher interest income. The year-over-year increase in other income and expense during 2013 was due primarily to higher interest and dividend income resulting from the Company’s higher cash, cash equivalents and marketable securities balances and lower premium expenses on foreign exchange contracts, partially offset by interest expense on debt issued in the third quarter of 2013 and higher expenses associated with foreign exchange rate movements. The weighted-average interest rate earned by the Company on its cash, cash equivalents and marketable securities was 1.11%, 1.03% and 1.03% during 2014, 2013 and 2012, respectively. The Company had no debt outstanding during 2012 and accordingly did not incur any related interest expense. 

The Company’s effective tax rates for all years differ from the statutory federal income tax rate of 35% due primarily to certain undistributed foreign earnings, a substantial portion of which was generated by subsidiaries organized in Ireland, for which no U.S. taxes are provided because such earnings are intended to be indefinitely reinvested outside the U.S. 

As of September 27, 2014, the Company had deferred tax assets arising from deductible temporary differences, tax losses and tax credits of $5.1 billion and deferred tax liabilities of $20.3 billion. Management believes it is more likely than not that forecasted income, including income that may be generated as a result of certain tax planning strategies, together with future reversals of existing taxable temporary differences, will be sufficient to fully recover the deferred tax