Practice supplies and other operating expenses increased $0.9 million, or 3.1%, to $31.8 million for the three months ended June 30, 2018, as compared to $30.9 million for the same period in 2017. The increase was primarily attributable to practice supply, rent and other costs related to our acquisitions, partially offset by decreases at our existing units.
General and administrative expenses include all billing and collection functions and all other salaries, benefits, supplies and operating expenses not specifically related to theday-to-day operations of our physician practices and services, as well as those attributable to ournon-physician service businesses. General and administrative expenses increased $4.9 million, or 4.8%, to $107.9 million for the three months ended June 30, 2018, as compared to $103.0 million for the same period in 2017. The increase of $4.9 million is attributable to the overall growth of the Company. Included within general and administrative expenses was an increase of $3.2 million of stock-based compensation expense primarily resulting from the change in timing of our annual equity grants from June to March in order to align the timing with other compensation related activities and a decrease of approximately $6.0 million in cost improvement as part of our corporate initiative. General and administrative expenses as a percentage of net revenue was 11.8% for the three months ended June 30, 2018, as compared to 12.2% for the same period in 2017.
Depreciation and amortization expense increased $0.8 million, or 3.0%, to $26.5 million for the three months ended June 30, 2018, as compared to $25.7 million for the same period in 2017. The increase was primarily attributable to the amortization of intangible assets related to acquisitions.
Income from operations increased $6.8 million, or 5.6%, to $128.7 million for the three months ended June 30, 2018, as compared to $121.9 million for the same period in 2017. Our operating margin was 14.1% for the three months ended June 30, 2018, as compared to 14.5% for the same period in 2017. The decrease of 41 basis points was primarily due to higher operating expense growth as compared to revenue growth.
Netnon-operating expenses were $19.1 million for the three months ended June 30, 2018, as compared to $17.5 million for the same period in 2017. The net increase innon-operating expenses was primarily related to an increase in interest expense due to higher average interest rates on higher outstanding borrowings under our credit agreement (the “Credit Agreement”).
Our effective income tax rate was 27.5% and 39.0% for the three months ended June 30, 2018 and 2017, respectively. The decrease in our effective tax rate is primarily related to the reduction in the corporate tax rate enacted under the Tax Cuts and Jobs Act of 2017.
Net income was $79.4 million for the three months ended June 30, 2018, as compared to $63.7 million for the same period in 2017. EBITDA was $157.7 million for the three months ended June 30, 2018, as compared to $148.7 million for the same period in 2017.
Diluted net income per common and common equivalent share was $0.85 on weighted average shares outstanding of 93.5 million for the three months ended June 30, 2018, as compared to $0.69 on weighted average shares outstanding of 92.8 million for the same period in 2017. Adjusted EPS was $1.07 for the three months ended June 30, 2018, as compared to $0.85 for the same period in 2017.
Six Months Ended June 30, 2018 as Compared to Six Months Ended June 30, 2017
Our net revenue increased $139.2 million, or 8.3%, to $1.82 billion for the six months ended June 30, 2018, as compared to $1.68 billion for the same period in 2017. Of this $139.2 million increase, $84.6 million, or 4.9%, was attributable to revenue generated from acquisitions completed after December 31, 2016 and $54.6 million, or 3.4%, was attributable to an increase in same-unit net revenue. Same units are those units at which we provided services for the entire current period and the entire comparable period. The increase in same-unit net revenue was comprised of a net increase of $28.7 million, or 1.8%, related to patient service volumes and an increase of $25.9 million, or 1.6%, from net reimbursement-related factors. The increase in revenue of $28.7 million from patient service volumes was related to growth across almost all of our services. The net increase in revenue of $25.9 million related to net reimbursement-related factors was primarily due to modest improvements in managed care contracting and an increase in the administrative fees received from our hospital partners, partially offset by a decrease in revenue caused by an increase in the percentage of our patients enrolled in GHC Programs.
Practice salaries and benefits increased $119.0 million, or 10.5%, to $1.25 billion for the six months ended June 30, 2018, as compared to $1.13 billion for the same period in 2017. This $119.0 million increase was primarily attributable to increased costs associated with physicians and other staff primarily to support organic-growth initiatives, acquisition-related growth and growth at our existing units, of which $96.9 million was related to salaries and $22.1 million was related to benefits and incentive compensation. We anticipate that we will continue to experience a higher rate of growth in compensation expense at our existing units over historic averages, which could adversely affect our business, financial condition, results of operations, cash flows and the trading price of our securities. We anticipate that practice salaries and benefits expense for the third and fourth quarters of 2018 will continue to include salaries and benefit costs for certain physicians who will remain employed through December 31, 2018 despite thenon-renewal of an anesthesia services contract with one of our hospital partners effective July 1, 2018, under which they had previously provided services.
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