based compensation awards may be granted. Shares subject to award under the 2019 Plan may be either authorized but unissued shares of our common stock or treasury shares. Refer to the Annual Report on Form 10-K for the year ended December 31, 2022 for further discussion on the 2019 Plan.

Compensation expense for stock-based awards recognized during the three months ended March 31, 2023 and 2022 was as follows (in thousands):


	Three Months Ended March 31,
		2023		2022
Stock options		$	768	$	173
Restricted stock units and awards		1,259		1,493
Performance share units		1,804		2,023
Total stock-based compensation expense		$	3,831	$	3,689

Stock Options and Restricted Stock Units and Awards – The following table presents our stock options and restricted stock units and awards activity during the three months ended March 31, 2023 (in thousands, except per share data):


	Stock Options			Restricted Stock Units and Awards
	Number of Options	Weighted Average Exercise Price Per Share		Number of Shares	Weighted Average Grant-Date Fair Value (1)
Outstanding at beginning of year	553	$	21.03	277	$	32.62
Granted	50	$	48.40	88	$	48.40
Exercised or released	(189)	$	19.20	(123)	$	29.87

Outstanding at March 31, 2023	414	$	25.16	242	$	39.76
Exercisable at March 31, 2023	414	$	25.16

(1)Represents weighted average market value of the shares; awards are granted at no cost to the recipients.

CBIZ utilized the Black-Scholes-Merton options pricing model to determine the fair value of stock options on the date of grant. The per-share fair value of stock options granted on February 8, 2023 was $15.35. The following weighted average assumptions were utilized:


			Three Months Ended March 31, 2023
Expected volatility (1)			28.57%
Expected option life (years) (2)			4.74
Risk-free interest rate (3)			3.89%
Expected dividend yield (4)			—%

(1) The expected volatility assumption was determined based upon the historical volatility of CBIZ's stock price using daily price intervals.

(2) The expected option life was determined based upon CBIZ's historical data using a midpoint scenario, which assumes all options are exercised halfway between the expiration date and the weighted average time it takes the option to vest.

(3) The risk-free interest rate assumption was based upon zero-coupon U.S. treasury bonds with a term approximating the expected life of the respective options.

(4) The expected dividend yield assumption was determined in view of CBIZ's historical and estimated dividend payouts.

Performance Share Units (“PSUs”) – PSUs are earned based on our financial performance over a contractual term of three years and the associated expense is recognized over that period based on the fair value of the award. A three-year cliff vesting schedule of the PSUs is dependent upon the Company’s performance relative to pre-established goals based on an earnings per share target

(weighted 70%) and total growth in revenue (weighted 30%). The fair value of PSUs is calculated using the market value of a share of our common stock on the date of grant. For performance achieved above specified levels, the recipient may earn additional shares of stock, not to exceed 200% of the number of PSUs initially granted.

The following table presents our PSU award activity during the three months ended March 31, 2023 (in thousands, except per share data):


	Performance Share Units	Weighted Average Grant-Date Fair Value Per Unit (1)
Outstanding at beginning of year	482	$	28.84
Granted	88	$	48.40
Vested	(244)	$	25.75


Outstanding at March 31, 2023	326	$	36.46

(1)Represents weighted average market value of the performance share units; PSUs are granted at no cost to the recipients.