9. Stock‑Based Compensation

The Company’s results of operations include expenses relating to stock‑based awards as follows (in thousands):



	Year Ended December 31,
	2019		2018		2017
Research and development	$	3,103	$	2,919	$	2,692
General and administrative		4,245		4,216		3,537
Total	$	7,348	$	7,135	$	6,229

Valuation Assumptions

The Company estimated the fair value of employee stock options using the Black-Scholes valuation model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of employee stock options were estimated using the following assumptions for the years ended December 31, 2019, 2018 and 2017:


	Year Ended December 31,
	2019		2018		2017
Risk-free interest rate	1.9	%	2.8	%	2.1	%
Expected volatility	82.1	%	82.7	%	91.4	%
Expected term (in years)	6.0		6.0		6.0
Expected dividend yield	0	%	0	%	0	%

Risk-free Interest Rate: The Company based the risk-free interest rate over the expected term of the options based on the constant maturity rate of U.S. Treasury securities with similar maturities as of the date of the grant.

Volatility: The Company used an average historical stock price volatility of comparable public companies within the biotechnology and pharmaceutical industry that have been identified as the Company’s industry peers.

Expected Term: The Company uses the simplified method prescribed in the ASC 718, Compensation—Stock Compensation, to calculate the expected term of options granted to employees and directors.

Expected Dividends: The Company has not paid and does not anticipate paying any dividends in the near future.

At December 31, 2019, 2018 and 2017, the unrecognized compensation expense associated with respect to options granted to employees was $13.4 million, $15.8 million and $18.6 million, respectively, and is expected to be recognized on a straight‑line basis over 2.71, 2.72, and 2.85 years, respectively.