The effect of recording stock-based compensation expense for the three and nine months ended September 30, 2026 and 2025 is as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2026		2025		2026		2025
Research and development	$	2,065	$	1,488		5,715		4,144
Selling, general and administrative		8,576		7,195		24,139		21,483
Total stock-based compensation expense	$	10,641	$	8,683	$	29,854	$	25,627

The Company uses a Monte Carlo simulation to determine the grant date fair value of performance stock awards subject to market conditions, or market-based PSUs. The following assumptions were used to value the performance stock awards subject to market conditions granted during the nine months ended September 30, 2026 and 2025:


	Nine Months Ended September 30,
	2026	2025
Expected life (years)	1.9 - 2.8		3.0
Risk-free interest rate	3.3% - 3.5%		3.9	%
Dividend yield	1.2% - 1.3%		1.5	%
Expected volatility	48.9% - 50.6%		46.4	%

Grants under the 2020 ESPP occur in June and December, as discussed in “Note 10 – Stockholders’ Equity”. The following assumptions were used to value the shares for these grants.


	Nine Months Ended September 30,
	2026			2025
Expected life (years)		2.0			2.0
Risk-free interest rate		4.1	%		3.9	%
Dividend yield		1.0	%		1.4	%
Expected volatility		54.1	%		46.0	%