Table:
| (In thousands, except per share amounts) | Number of Shares | Weighted Average Grant Date Fair Value |
| --- | --- | --- |
| Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2018 | 1,570 | $18.52 |
| PSUs, RSUs and restricted stock granted | 897 | $9.63 |
| PSUs, RSUs and restricted stock vested | (368) | $17.23 |
| PSUs, RSUs and restricted stock forfeited | (208) | $18.24 |
| Unvested RSUs and restricted stock outstanding, December 31, 2019 | 1,891 | $14.58 |
Paragraphs:
PSUs, RSUs and restricted stock
Under the 2015 Plan, awards other than stock options, including PSUs, RSUs and restricted stock, may be granted to certain employees and officers.
Under our market-based PSU program, the number of shares of common stock earned by a recipient is subject to a market condition based on ADTRAN’s relative total shareholder return against all companies in the NASDAQ Telecommunications Index at the end of a three-year performance period. Depending on the relative total shareholder return over the performance period, the recipient may earn from 0% to 150% of the shares underlying the PSUs, with the shares earned distributed upon the vesting. The fair value of the award is based on the market price of our common stock on the date of grant, adjusted for the expected outcome of the impact of market conditions using a Monte Carlo Simulation valuation method. A portion of the granted PSUs vests and the underlying shares become deliverable upon the death or disability of the recipient or upon a change of control of ADTRAN, as defined by the 2015 Plan. The recipients of the PSUs receive dividend credits based on the shares of common stock underlying the PSUs. The dividend credits vest and are earned in the same manner as the PSUs and are paid in cash upon the issuance of common stock for the PSUs.
During the first quarter of 2017, the Compensation Committee of the Board of Directors approved a one-time PSU grant of 0.5 million shares that contained performance conditions and would have vested at the end of a three-year period if such performance conditions were met. The fair value of these performance-based PSU awards was equal to the closing price of our stock on the date of grant. These awards were forfeited during the first quarter of 2020 as the performance conditions were not achieved.
The fair value of RSUs and restricted stock is equal to the closing price of our stock on the business day immediately preceding the grant date. RSUs and restricted stock vest ratably over four-year and one-year periods, respectively.
We will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. If circumstances change, and additional data becomes available over time, we may change our assumptions and methodologies, which may materially impact our fair value determination.
The following table is a summary of our PSUs, RSUs and restricted stock outstanding as of December 31, 2018 and 2019 and the changes that occurred during 2019:
Question:
What was the change in Unvested RSUs and restricted stock outstanding between 2018 and 2019?
Answer: 1891-1570 = 321