NOTE 7. EQUITY INCENTIVE PLANS

Stock Option Plan

During the three months ended March 31, 2020, options were granted to employees to purchase 1,919,789 shares. The weighted-average grant-date estimated fair value of options granted during the three months ended March 31, 2020 was $5.27. The estimated grant date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following weighted-average assumptions:


	Three Months Ended March 31,
	2020
Expected term (years)	6.00
Expected volatility	83.62	%
Risk-free interest rate	1.68	%
Dividend yield	—	%

During the three months ended March 31, 2020 and 2019, options were exercised to purchase 141,551 and 770 shares, respectively, of the Company's common stock, resulting in approximately $0.2 million and insignificant net proceeds to the Company in the three months ended March 31, 2020 and 2019, respectively.

Restricted Stock Units (“RSUs”)

In July 2018, the Company granted 903,374 performance-based restricted stock units (“PRSUs”) to its employees that vest upon the achievement of certain performance conditions, subject to the employees’ continued service relationship with the Company through the achievement date. As of March 31, 2020, 849,328 of these PRSUs were outstanding and none of these PRSUs were vested. Based on the evaluation of the performance conditions, the Company recorded stock-based compensation expense of $0.9 million and zero for the three months ended March 31, 2020 and 2019, respectively. The related compensation cost is recognized as an expense ratably over the estimated vesting period. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted.

No RSUs or PRSUs were granted during the three months ended March 31, 2020 or 2019. Similarly, no common shares were issued upon vesting of time-based RSUs during these periods.

Employee Stock Purchase Plan

In February 2020, the Company sold 75,804 shares of its common stock under the Company’s employee stock purchase program (“ESPP”). The shares were purchased by employees at a purchase price of $4.95 per share with proceeds to the Company of approximately $0.4 million.

Stock-Based Compensation

Stock-based compensation expense recognized for stock options, RSUs, PRSUs and the Company’s ESPP are recorded as operating expenses in the Company’s condensed statements of operations and comprehensive loss, as follows:


	Three Months Ended March 31,
	2020		2019

Research and development	$	1,058	$	760
General and administrative		1,890		1,162
Total	$	2,948	$	1,922

As of March 31, 2020, the Company’s total unrecognized stock-based compensation expense, net of estimated forfeitures, and average remaining vesting period, included the following:


	Unrecognized Compensation Expense		Average Remaining Vesting Period (Years)
Stock options	$	13,401	3.0
PRSUs	$	602	0.4
ESPP	$	194	0.4