Regulatory, connectivity and produced content costs remained constant and decreased during the three and nine months ended September 30, 2020, respectively, due to deferred sports rights costs associated with the shortened baseball season resulting from COVID-19.
Charter’s Adjusted OIBDA for the three and nine months ended September 30, 2020 increased for the reasons described above.
Depreciation and amortization expense decreased $45 million and $170 million during the three and nine months ended September 30, 2020, respectively, as compared to the corresponding periods in the prior year primarily due to a decrease in depreciation and amortization as certain assets acquired in acquisitions become fully depreciated offset by an increase in depreciation as a result of more recent capital expenditures.
Charter’s results were also impacted by other expenses, net which increased $70 million and $243 million for the three and nine months ended September 30, 2020, respectively, as compared to the corresponding periods in the prior year. The increase in other expenses, net for the three months ended September 30, 2020, as compared to the corresponding period in the prior year, was primarily due to increased other pension costs and a loss on extinguishment of debt, partially offset by increased gains on financial instruments. The increase in other expenses, net for the nine months ended September 30, 2020, as compared to the corresponding period in the prior year, was primarily due to increased other pension costs and a loss on extinguishment of debt, partially offset by a decrease to other expense.
Income tax expense increased $51 million and $43 million for the three and nine months ended September 30, 2020, respectively, as compared to the corresponding periods in the prior year. Income tax expense increased during the three and nine months ended September 30, 2020 compared to the corresponding periods in 2019 primarily as a result of higher pretax income offset by increased recognition of excess tax benefits resulting from share-based compensation during 2020.
Gain (loss) on dilution of investment in affiliate
The loss on dilution of investment in affiliate increased by $24.1 million and $71.7 million during the three and nine months ended September 30, 2020, respectively, as compared to the corresponding periods in the prior year, primarily due to an increase in issuance of Charter common stock from the exercise of stock options held by employees and other third parties, at prices below Liberty Broadband’s book basis per share. As Liberty Broadband’s ownership in Charter changes due to exercises of Charter stock options, a loss is recorded with the effective sale of common stock, because the exercise price of Charter stock options is typically lower than the book value of the Charter shares held by Liberty Broadband.
Realized and unrealized gains (losses) on financial instruments, net
Realized and unrealized gains (losses) on financial instruments, net for the three and nine months ended September 30, 2020, were primarily related to changes in fair value of the Debentures related to changes in market price of underlying Charter stock. Realized and unrealized gains (losses) on financial instruments, net for the three and nine months ended September 30, 2019, were related to the zero-strike call options. See discussion in note 3 to the accompanying condensed consolidated financial statements for additional information.
Other, net
Other, net decreased $0.3 million and $1.0 million during the three and nine months ended September 30, 2020, respectively, as compared to the corresponding periods in the prior year. The decreases were primarily due to decreases in dividend and interest income as a result of lower interest rates and lower cash balances during the current year.
Income tax benefit (expense)
During the three and nine months ended September 30, 2020, we had an income tax expense of $25.0 million and $47.2 million, respectively, and the effective rate was approximately 26.6% and 26.1%. For the three and nine months ended September 30, 2019, we had an income tax expense of $9.1 million and $8.5 million, respectively, and the effective tax rate was approximately 24.9% and 25.1%, respectively. The differences between the effective income tax rates and the U.S.