Aimco and the Aimco Operating Partnership calculate basic earnings per common share and basic earnings per common unit based on the weighted average number of shares of Common Stock and common partnership units outstanding and excludes participating securities. Diluted earnings per share and diluted earnings per unit are calculated taking into consideration dilutive common stock and common partnership unit equivalents and dilutive convertible securities outstanding during the period.

Our common stock and common partnership unit equivalents include options to purchase shares of Common Stock, which, if exercised, would result in Aimco’s issuance of additional shares and the Aimco Operating Partnership’s issuance to Aimco of additional common partnership units equal to the number of shares purchased under the options. These equivalents also include unvested total stockholder return, or TSR, restricted stock awards that do not meet the definition of participating securities, which would result in an increase in the number of shares of Common Stock and common partnership units outstanding equal to the number of shares that vest. Common partnership unit equivalents also include unvested long-term incentive partnership units. Securities with dilutive effect are included in the denominator for calculating diluted earnings per share and per unit during these periods.

Our time-based restricted stock awards receive non-forfeitable dividends similar to shares of Common Stock and common partnership units prior to vesting. These dividends and distributions are not forfeited if the awards fail to vest. Therefore, the unvested shares and units related to these awards are participating securities. The effect of our time-based restricted stock awards is included in basic and diluted earnings per share and unit computations using the two-class method of allocating distributed and undistributed earnings when the two-class method is more dilutive than the treasury method.

The effect of dilutive securities included in the calculation of earnings per share, and securities not dilutive and excluded from the calculation of earnings per share, for the three and nine months ended September 30, 2019 and 2018, were as follows (in thousands):

	Three Months Ended		Nine Months Ended
	September 30, 2019	September 30, 2018	September 30, 2019	September 30, 2018
Dilutive share equivalents outstanding	202	222	218	158
Dilutive partnership unit equivalents outstanding	261	240	327	165
Non-dilutive share equivalents outstanding	—	184	—	184
Non-dilutive partnership unit equivalents outstanding	—	421	—	421
Unvested restricted participating shares and partnership units	189	250	189	250

The Aimco Operating Partnership has various classes of preferred OP Units, which may be redeemed at the holder’s option. The Aimco Operating Partnership may redeem these units for cash, or at its option, shares of Common Stock. As of September 30, 2019, these preferred OP Units were potentially redeemable for approximately 1.9 million shares of Common Stock (based on the period end market price), or cash. The Aimco Operating Partnership has a redemption policy that requires cash settlement of redemption requests for the preferred OP Units, subject to limited exceptions. Accordingly, we have excluded these securities from earnings per share and unit computations and we expect to exclude them in future periods.

During the three and nine months ended September 30, 2019, we paid $0.39 and $2.80, respectively, in dividends and distributions per share and per unit. Of the $2.80 paid in dividends and distributions in 2019, $2.02 was paid in March and represents the per share and unit value of the special dividend and special distribution. The special dividend consisted of $67.1 million in cash, 4.5 million shares of Common Stock and $0.4 million of cash paid in lieu of issuing fractional shares. The special distribution consisted of $72.7 million in cash, 4.8 million common partnership units and $0.4 million of cash paid in lieu of issuing fractional units. During the three and nine months ended September 30, 2018, we paid $0.38 and $1.14, respectively, in dividends and distributions per share and per unit.