Note 4 – Stock-based Compensation

We did not grant any stock options to employees or non-employees during the three months ended March 31, 2020 or 2019. At March 31, 2020, we had outstanding options to purchase 175,466 shares of our common stock of which options for the purchase of 34,557 shares of our common stock were vested. We recorded $98,663 and $58,559 of stock-based compensation expense for the three months ended March 31, 2020 and 2019, respectively.