General and Administrative.General and administrative expenses decreased by $2.3 million to $12.4 million for the three months ended September 30, 2019 from $14.7 million for the three months ended September 30, 2018. General and administrative costs decreased due to reduced legal cost attributable to settlement of the GX Dispute during the second quarter of 2019 and other cost reductions.
Income Tax Expense.Our effective income tax rates were 137.1% and (12.6%) for the three months ended September 30, 2019 and 2018, respectively. Our effective tax rate is affected by factors including changes in valuation allowances, fluctuations in income across jurisdictions with varying tax rates, and changes in income tax reserves, including related penalties and interest.
Nine months Ended September 30, 2019 and 2018
Revenue.Revenue increased by $0.2 million, or 0.1%, to $178.8 million for the nine months ended September 30, 2019 from $178.6 million for the nine months ended September 30, 2018, driven by growth in the Apps & IoT segment. Revenue for the Apps & IoT segment increased $5.9 million, or 30.5%, due to our focus on growth of the application layer and IoT space. Revenue for the Systems Integration segment decreased $2.6 million, or 8.4%. Revenue for the MCS segment decreased $3.1 million, or 2.4%.
Cost of Revenue (excluding depreciation and amortization).Cost of revenue (excluding depreciation and amortization) decreased by $2.0 million, or 1.8%, to $108.6 million for the nine months ended September 30, 2019 from $110.7 million for the nine months ended September 30, 2018. Cost of revenue (excluding depreciation and amortization) decreased in the MCS segment by $2.8 million from cost reductions. Cost of revenue (excluding depreciation and amortization) decreased in the Systems Integration segment by $2.3 million. Cost of revenue (excluding depreciation and amortization) increased in the Apps & IoT segment by $3.0 million as we continue our strategy to grow our application layer and IoT space, including Intelie.
Depreciation and Amortization.Depreciation and amortization expense decreased by $1.0 million to $23.8 million for the nine months ended September 30, 2019 from $24.8 million for the nine months ended September 30, 2018. The decrease is primarily attributable to the intangibles from the July 2012 acquisition of Nessco being fully amortized coupled with lower capital expenditures.
Selling and Marketing.Selling and marketing expense decreased $0.3 million to $9.5 million for the nine months ended September 30, 2019 from $9.9 million for the nine months ended September 30, 2018.
General and Administrative.General and administrative expenses increased by $2.2 million to $43.3 million for the nine months ended September 30, 2019 from $41.1 million for the nine months ended September 30, 2018. General and administrative costs increased primarily due to increased stock-based compensation and increased GX Dispute legal expenses.
Income Tax Expense.Our effective income tax rates were (47.0%) and 0.1% for the nine months ended September 30, 2019 and 2018, respectively. Our effective tax rate is affected by factors including changes in valuation allowances, fluctuations in income across jurisdictions with varying tax rates, and changes in income tax reserves, including related penalties and interest.
Liquidity and Capital Resources
At September 30, 2019, we had working capital, including cash and cash equivalents, of $26.9 million.
Based on our current expectations, we believe our liquidity and capital resources will be sufficient for the conduct of our business and operations for the foreseeable future. We may also use a portion of our available cash to pay down outstanding debt.
During the next twelve months, we expect our principal sources of liquidity to be cash flows from operating activities, cash and cash equivalents on hand and availability under our Credit Agreement.
While we believe we have sufficient liquidity and capital resources to meet our current operating requirements and our growth plans, we may elect to pursue expansion opportunities within the next year which could require additional financing, either debt or equity.
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