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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)
3 Months Ended
Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]  
Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options and employee stock purchases for the three months ended March 31, 2021 and 2020, which was allocated as follows:

 

 

 

Three Months Ended March 31,

 

(In thousands)

 

2021

 

 

2020

 

Research and development

 

$

825

 

 

$

501

 

General and administrative

 

 

969

 

 

 

1,067

 

Stock-based compensation expense included in operating expenses

 

$

1,794

 

 

$

1,568

 

 

Schedule of assumptions used to estimate the fair value of service-based stock options granted The fair value of service-based options granted during the three months ended March 31, 2021 and 2020 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:

 

 

 

Three Months Ended March 31,

 

 

 

2021

 

2020

 

Dividend yield

 

0%

 

0%

 

Expected volatility range

 

0.779 to 0.783

 

 

0.781

 

Risk-free interest rate range

 

0.51% to 0.94%

 

1.42% to 1.62%

 

Expected term

 

5.5 yrs

 

5.25 yrs

 

Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan

The fair value of employees’ purchase rights during the three months ended March 31, 2021 and 2020 has been estimated using the Black Scholes option-pricing model with the following assumptions:

 

 

 

Three Months Ended March 31,

 

 

2021

 

2020

Dividend yield

 

0%

 

0%

Expected volatility range

 

0.507 to 0.680

 

0.478 to 0.564

Risk-free interest rate range

 

0.09% to 0.16%

 

1.56% to 1.57%

Expected term range

 

6 mos to 12 mos

 

6 mos to 12 mos