Summary of Assumptions Used in Black-Scholes Option Pricing Model


	Three Months Ended		Six Months Ended
	June 30,		June 30,
	2020	2019	2020	2019
Risk-free interest rate	0.42% - 0.54%	1.95% - 2.36%	0.42% - 1.57%	1.95% - 2.62%
Expected volatility	73.73% - 74.80%	73.06% - 73.78%	73.72% - 74.80%	73.06% - 75.19%
Expected dividend yield	0%	0%	0%	0%
Expected life of employee options (in years)	6.25	6.25	6.25	6.25
Expected life of non-employee options (in years)	—	—	—	—

A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the six months ended June 30, 2020 is presented below:


		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2019	4,450,517	$	14.73
Granted	820,350		16.04
Exercised	(24,346)		11.34
Expired	(167,964)		13.85
Forfeited	(113,791)		16.21
Outstanding, June 30, 2020	4,964,766	$	14.96
Options exercisable, June 30, 2020	2,756,734

Summary of Assumptions Used in Black-Scholes Option Pricing Model

On January 1, 2019, the Company used the Black-Scholes option valuation model to remeasure the fair value of all outstanding unvested options that had been granted to non-employee consultants in accordance with ASU 2018-07, Compensation – Stock Compensation (Topic 718), Improvements to Non-employee Share-Based Payment Accounting. The range of assumptions used by the Company on January 1, 2019 were as follows:



		January 1, 2019
Risk-free interest rate		2.59% - 2.62%
Expected volatility		58.9% - 84.6%
Expected dividend yield		0%
Expected life of non-employee options (in years)		0.81 - 8.19