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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)
3 Months Ended
Mar. 31, 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 months ended March 31, 2019 and 2018 which was allocated as follows:

 

 

Three Months Ended March 31,

 

(In thousands)

 

2019

 

 

2018

 

Research and development

 

$

240

 

 

$

155

 

General and administrative

 

 

1,186

 

 

 

1,459

 

Stock-based compensation expense included in operating expenses

 

$

1,426

 

 

$

1,614

 

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 three months ended March 31, 2019 and 2018 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:

 

 

Three Months Ended March 31,

 

 

 

2019

 

2018

 

Dividend yield

 

0%

 

0%

 

Expected volatility range

 

0.925 to 0.980

 

0.821

 

Risk-free interest rate range

 

2.24% to 2.56%

 

2.55%

 

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 three months ended March 31, 2019 and 2018 has been estimated using the Black Scholes option-pricing model with the following assumptions:

 

 

Three Months Ended March 31,

 

 

2019

 

2018

Dividend yield

 

0%

 

0%

Expected volatility range

 

1.333 to 1.653

 

0.437 to 0.475

Risk-free interest rate range

 

2.56% to 2.63%

 

1.53% to 1.76%

Expected term range

 

6 mos to 12 mos

 

6 mos to 12 mos