Stock-Based Compensation. The following table presents stock-based employee compensation expenses included in our unaudited consolidated statements of comprehensive income (in thousands):

	Three Months Ended March 31,
	2018		2017

Cost of services	$	-	$	2
Research and development		5		12
Selling and marketing		1		1
General and administrative		18		56
Stock-based compensation expense	$	24	$	71

Stock Option Grants. We may grant stock options under our 2001 Nonqualified Stock Plan although we have not granted any stock options since the first quarter of 2012. When we grant stock options, we estimate their fair value using the Black-Scholes valuation model. This valuation model takes into account the exercise price of the award, as well as a variety of significant assumptions. The assumptions used to estimate the fair value of stock options include the expected term, the expected volatility of our stock over the expected term, the risk-free interest rate over the expected term, and our expected annual dividend yield. We believe that the valuation technique and the approach utilized to develop the underlying assumptions are appropriate in calculating the fair values of our stock options. Estimates of fair value are not intended to predict actual future events or the value ultimately realized by persons who receive equity awards.

Unrestricted Stock Grants. We also grant unrestricted shares of stock under our 2001 Nonqualified Stock Plan. Stock-based compensation expense for stock grants is determined based on the fair market value of our stock on the date of grant, provided the number of shares in the grant is fixed on the grant date.

We granted shares of unrestricted stock in 2018 and 2017 that affected financial results for the three month periods ended March 31, 2018 and 2017. These grants are described below.

2018 Grant. On March 20, 2018, we granted 138,000 shares of unrestricted stock to directors, officers and employees. The shares will be issued in two equal installments shortly after June 30, 2018 and December 31, 2018, provided each grantee is serving as a director, officer or employee on those dates. The total stock-based compensation expense related to this grant is $580,000, of which $24,000 was charged to expense in the three months ended March 31, 2018 and we anticipate the remaining $556,000 will be charged to expense ratably over the remaining three quarters of 2018.

2017 Grant. In February 2017, we granted 134,000 shares of unrestricted stock to directors, officers and employees. The shares were issued in two equal installments shortly after June 30, 2017 and December 31, 2017. We expensed the entire $663,000 stock-based compensation expense related to this grant in 2017. We issued shares of common stock related to this grant as follows: i) 54,014 net shares of common stock were issued in early July 2017 after employees surrendered 12,986 shares for which we paid $67,000 of withholding taxes on their behalf; and ii) 53,378 net shares of common stock were issued in early January 2018 after employees surrendered 13,622 shares for which we paid $64,000 of withholding taxes on their behalf.