General and Administrative.General and administrative expenses increased by $1.7 million to $14.5 million for the three months ended June 30, 2019 from $12.8 million for the three months ended June 30, 2018. General and administrative costs increased primarily due to GX dispute legal costs and stock-based compensation.
Income Tax Expense.Our effective income tax rates were (56.2%) and 17.7% for the three months ended June 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.
Six Months Ended June 30, 2019 and 2018
Revenue.Revenue increased by $4.0 million, or 3.5%, to $117.8 million for the six months ended June 30, 2019 from $113.8 million for the six months ended June 30, 2018, driven by growth in the Apps & IoT segment including the 2018 acquisitions of Intelie along with the 2018 acquisitions of Auto-Comm and SAFCON, which is primarily in the Systems Integration Segment. Revenue for the Apps & IoT segment increased $4.1 million, or 34.5%, due to our focus on growth of the application layer and IoT space, including $1.8 million from the acquisition of Intelie and $0.7 million from the acquisition of Auto-Comm and SAFCON. Revenue for the Systems Integration segment increased $0.1 million, or 0.6%, which included $2.1 million from the acquisition of Auto-Comm and SAFCON.
Cost of Revenue (excluding depreciation and amortization).Cost of revenue (excluding depreciation and amortization) increased by $3.0 million, or 4.4%, to $73.0 million for the six months ended June 30, 2019 from $69.9 million for the six months ended June 30, 2018. Cost of revenue (excluding depreciation and amortization) increased in the Apps & IoT segment by $2.6 million as we continue our strategy to grow our application layer and IoT space including Intelie. Cost of revenue (excluding depreciation and amortization) increased in the MCS segment by $1.0 million as a result of our increased site count during the period. Cost of revenue (excluding depreciation and amortization) decreased in the Systems Integration segment by $0.5 million.
Depreciation and Amortization.Depreciation and amortization expense increased by $0.2 million to $16.6 million for the six months ended June 30, 2019 from $16.3 million for the six months ended June 30, 2018. The increase is primarily attributable to additions to property, plant and equipment and intangibles from acquisitions and capital expenditures.
Selling and Marketing.Selling and marketing expense decreased $0.4 million to $6.7 million for the six months ended June 30, 2019 from $7.1 million for the six months ended June 30, 2018. This decrease was due to cost reductions.
General and Administrative.General and administrative expenses increased by $4.5 million to $30.9 million for the six months ended June 30, 2019 from $26.4 million for the six months ended June 30, 2018. General and administrative costs increased primarily due to increased stock-based compensation, increased GX dispute legal costs, restructuring costs and expenses attributable to a full period of operations of the 2018 acquisitions of Intelie, Auto-Comm and SAFCON.
Income Tax Expense.Our effective income tax rates were (36.9%) and 3.2% for the six months ended June 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 June 30, 2019, we had working capital, including cash and cash equivalents, of $23.8 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 finance growth through the acquisition of, or investment in, businesses, products, services or technologies complementary to our current business, through mergers, acquisitions, joint ventures or otherwise, or 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 expansion plans, we may elect to pursue additional expansion opportunities within the next year or we may require additional liquidity for contingent liabilities, which could require additional financing, either debt or equity.
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