offset by an increase in payroll expense of $97,000. We expect that research and development costs will increase in the future as we invest in improvements to existing products as well as development of new products.
Other income (expense). We incur interest expense in connection with our secured credit facility with Silicon Valley Bank.
Year ended December 31, 2014 compared to the year ended December 31, 2013
Total revenue. Total revenue was $5,810,205 for the year ended December 31, 2014 compared to $10,478,920 for the year ended December 31, 2013, a decrease of $4,668,715 or 44.6%. The decrease in revenue was primarily due to significantly fewer systems sold in 2014 due to uncertainty regarding reimbursement to our customers for the use of our products. Average selling price in 2014 did not change significantly compared to 2013.
Total cost of sales. Cost of sales was $2,054,798 for the year ended December 31, 2014 compared to $3,600,348 for the year ended December 31, 2013, a decrease of $1,545,550 or 42.9% due to the lower sales in 2014 compared to 2013.
Gross profit. Gross profit was $3,755,407 for the year ended December 31, 2014 compared to $6,878,572 for the year ended December 31, 2013, a decrease of $3,123,165, or 45.4%, for the reasons discussed above. Our gross profit percentage was 64.6% in 2014 compared to 65.6% in 2013.
Selling and marketing. Selling and marketing expense was $4,208,241 for the year ended December 31, 2014 compared to $3,965,276 for the year ended December 31, 2013, an increase of $242,965 or 6.1%. The net increase was mainly due to higher spending on trade shows ($448,000) and marketing consultants ($256,000), offset by lower payroll ($416,000) due to headcount reductions during 2014 and lower travel ($51,000).
General and administrative. General and administrative expense was $1,650,651 for the year ended December 31, 2014 compared to $1,453,344 for the year ended December 31, 2013, an increase of $197,307 or 13.6%. The net increase was due primarily to higher legal expenses ($251,000) and bad debt expense ($128,000), offset by lower payroll ($146,000).
Research and development. Research and development expense was $1,576,775 for the year ended December 31, 2014 compared to $1,333,111 for the year ended December 31, 2013, an increase of $243,664, or 18.3%. The increase was mostly research and development ($116,000) attributable to the enhanced SRT-100 Vision product and foreign registrations ($126,000).
Other income (expense). We incur interest expense in connection with our secured credit facility with Silicon Valley Bank.
Seasonality
We do not believe our business to be seasonal in nature.
Liquidity and capital resources
Overview
As of December 31, 2015, we had cash and cash equivalents of $5,065,068 and an accumulated deficit of $(7,445,809) compared to cash and cash equivalents of $4,538,713 and an accumulated deficit of $(7,208,542) as of December 31, 2014.
Our liquidity position and capital requirements may be impacted by a number of factors, including the following:
| • | our ability to generate and increase revenue; |
| • | fluctuations in gross margins, operating expenses and net loss; and |
| • | fluctuations in working capital. |
Our primary short-term capital needs, which are subject to change, include expenditures related to: