Military. Military selling, general and administrative expenses remained relatively consistent in 2019, as compared to 2018.
Multifamily. Multifamily selling, general and administrative expenses increased $6.3 million, or 166.1%, in 2019, as compared to 2018, primarily due to a $5.7 million increase in personnel related expenses, a $0.3 million increase in travel and entertainment expenses, a $0.2 million increase in cloud services, a $0.2 million increase in hardware and software maintenance expenses, and a $0.2 million increase in rent and facilities expenses. These increases were partially offset by a $1.0 million decrease in the fair value of contingent consideration. Our Multifamily business was acquired in August 2018.
Legacy. Legacy selling, general and administrative expenses decreased $6.1 million, or 21.0%, in 2019, as compared to 2018, primarily due to a $4.9 million decrease in personnel related expenses and a $1.2 million decrease in depreciation expense.
Private networks and emerging technologies. Private networks and emerging technologies selling, general and administrative expenses remained relatively consistent in 2019, as compared to 2018.
Corporate. Corporate selling, general and administrative expenses increased $3.3 million, or 6.3%, in 2019, as compared to 2018, primarily due to a $1.4 million increase in restructuring charges, a $1.1 million increase in depreciation expense, and a $1.1 million increase in hardware and software maintenance. These increases were partially offset by a $0.5 million decrease in consulting expenses.
Amortization of Intangible Assets
Amortization of intangible assets expense increased $0.9 million, or 23.2%, in 2019, as compared to 2018, primarily due to a $1.6 million increase in multifamily amortization of intangible assets resulting from our Elauwit acquisition in August 2018. This increase was offset by a $0.6 million decrease in carrier services amortization of intangible assets resulting from the full amortization of certain intangible assets in 2018.
Interest Expense and Amortization of Debt Discount
Interest expense and amortization of debt discount increased $6.2 million in 2019, as compared to 2018, primarily due to interest expense incurred in connection with the Convertible Notes we issued in October 2018. During 2019 and 2018, we capitalized $3.3 million and $1.1 million, respectively, of interest expense.
Interest Income and Other Expense, Net
Interest income and other expense, net increased $1.5 million in 2019, as compared to 2018, primarily due to increased interest income related to our cash equivalents and marketable securities balances in 2019.
Income Tax Benefit
Income tax benefit decreased $5.1 million in 2019, as compared to 2018. In 2019, our effective tax rate was 0.3%. In 2018, our effective tax rate was 105.5%, which included a $5.7 million benefit related to the reversal of our valuation allowance for the tax effect on the equity component of our Convertible Notes. Our effective tax rate also differs from the statutory rate primarily due to our valuation allowance for the years ended December 31, 2019 and 2018, as well as minimum state taxes and foreign tax expense for the year ended December 31, 2018. Income tax benefit for the year ended December 31, 2018 included an increase of $0.4 million resulting from the adoption of ASC 606 as of January 1, 2018.
Non-controlling Interests
Non-controlling interests decreased $1.5 million, or 98.7%, in 2019, as compared to 2018 resulting from decreased net income for a subsidiary from DAS build-out projects that were completed in 2018.
Net Loss Attributable to Common Stockholders
Our net loss attributable to common stockholders in 2019 increased $9.1 million as compared to 2018, primarily due to the $13.7 million increase in costs and operating expenses, the $6.2 million increase in interest expense and amortization of debt discount, and the $5.1 million decrease in income tax benefit, which were partially offset by the $13.0 million increase in revenues, the $1.5 million increase in interest income and other expense, net, and the $1.5