Depreciation and amortization expense decreased $67 million and $319 million during the three and nine months ended September 30, 2019, respectively, as compared to the corresponding periods in the prior year. The decreases were primarily due to a decrease in depreciation and amortization as certain assets acquired from Time Warner Cable, Inc. (“TWC” or “Legacy TWC”) and Bright House Networks, LLC becoming fully depreciated offset slightly by an increase in depreciation as a result of more recent capital expenditures.
Charter’s results were also impacted by an increase in other expenses, net of $306 million and $595 million for the three and nine months ended September 30, 2019, respectively. The increase in other expenses, net for the three and nine months ended September 30, 2019, as compared to the corresponding periods in the prior year, was primarily as a result of decreased net other pension benefits of $198 million and $220 million, respectively, primarily due to a remeasurement gain in the third quarter of 2018 as a result of significant lump sum settlement payments to participants. Additionally, interest expense, net increased by $62 million and $203 million, for the three and nine months ended September 30, 2019, as compared to the corresponding periods in the prior year, respectively. Charter also recorded increased losses on financial instruments of $46 million and $116 million for the three and nine months ended September 30, 2019, respectively, compared to the corresponding periods in 2018.
Income tax expense increased $17 million and $151 million for the three and nine months ended September 30, 2019, respectively, as compared to the corresponding periods in the prior year. Income tax expense increased year over year primarily as a result of higher pretax income and lower benefit from state tax law changes.
Gain (loss) on dilution of investment in affiliate
The loss on dilution of investment in affiliate increased by $8.0 million and $33.8 million during the three and nine months ended September 30, 2019, 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 on financial instruments, net for the three and nine months ended September 30, 2019 and 2018, were related to the zero-strike call options (see discussion in note 3 to the accompanying condensed consolidated financial statements).
Other, net
Other, net increased $0.1 million and $0.5 million during the three and nine months ended September 30, 2019, respectively, as compared to the corresponding periods in the prior year. The increases were primarily due to increases in dividend and interest income as a result of higher interest rates in the current year.
Income tax benefit (expense)
During 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 rate was approximately 24.9% and 25.1%, respectively. For the three and nine months ended September 30, 2018, we had an income tax expense of $17.8 million and $17.0 million and the effective tax rate was approximately 22.9% and 23.6%, respectively. The difference between the effective income tax rate of 24.9% and the U.S. Federal income tax rate of 21% for the three months ended September 30, 2019 was primarily due to the effect of state income taxes. The difference between the effective income tax rate of 25.1% and the U.S. Federal income tax rate of 21% for the nine months ended September 30, 2019 was primarily due to the effect of state income taxes. The difference between the effective income tax rate of 22.9% and the U.S. Federal income tax rate of 21% for the three months ended September 30, 2018 was primarily due to the effect of state income taxes, partially offset by unrealized gains attributable to the Company’s own stock which is not recognized for tax purposes. The difference between the effective income tax rate of