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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)
9 Months Ended
Sep. 30, 2019
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 and nine months ended September 30, 2019 and 2018, which was allocated as follows:

 

 

Three Months Ended September 30,

 

 

Nine Months Ended September 30,

 

(In thousands)

 

2019

 

 

2018

 

 

2019

 

 

2018

 

Research and development

 

$

518

 

 

$

269

 

 

$

1,171

 

 

$

690

 

General and administrative

 

 

1,051

 

 

 

1,346

 

 

 

3,258

 

 

 

4,084

 

Stock-based compensation expense included in operating expenses

 

$

1,569

 

 

$

1,615

 

 

$

4,429

 

 

$

4,774

 

Schedule of assumptions used to estimate the fair value of service-based and performance-based stock options granted The fair value of service-based and performance-based options granted during the nine months ended September 30, 2019 and 2018 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:

 

 

Nine Months Ended September 30,

 

 

2019

 

2018

Dividend yield

 

0%

 

0%

Expected volatility range

 

0.793 to 0.980

 

0.821 to 0.832

Risk-free interest rate range

 

1.50% to 2.56%

 

2.55% to 2.94%

Expected term range

 

5.25 yrs to 6.44 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 nine months ended September 30, 2019 and 2018 has been estimated using the Black Scholes option-pricing model with the following assumptions:

 

 

Nine Months Ended September 30,

 

 

2019

 

2018

Dividend yield

 

0%

 

0%

Expected volatility range

 

0.646 to 1.653

 

0.437 to 0.475

Risk-free interest rate range

 

1.94% to 2.63%

 

1.53% to 1.76%

Expected term range

 

6 mos to 12 mos

 

6 mos to 12 mos