Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations - (continued)
June 30, 2016, respectively. The change in expense for the three and six months ended June 30, 2017 resulted primarily from:
an increase of $0.1 million and $2.4 million, respectively, in other operating expenses at our 2017 same-center group;
centers acquired or opened during 2016, which resulted in an increase of $1.0 million and $2.6 million, respectively;
centers acquired during 2017, which resulted in an increase of $0.4 million and $0.6 million, respectively;
deconsolidation of centers in the prior period, which resulted in a decrease of $1.1 million and $1.3 million, respectively; and
disposal of centers in the current and prior periods, which resulted in a decrease of $1.5 million and $2.7 million, respectively.
Transaction costs were approximately $3.0 million and $5.3 million for the three and six months ended June 30, 2017, respectively, and $2.1 million and $2.3 million for the three and six months ended June 30, 2016, respectively, primarily resulting from the Merger, as well as our acquisition of surgery centers during the current period.
Depreciation and amortization expense remained relatively unchanged at 3.1% and 2.8% of net revenue for the three and six months ended June 30, 2017 and 2016, respectively.
Equity in earnings of unconsolidated affiliates was $6.1 million and $11.3 million during the three and six months ended June 30, 2017, respectively, and $5.3 million and $9.1 million during the three and six months ended June 30, 2016, respectively. The increase in our earnings from equity method investments during the three and six months ended June 30, 2017 is due to the consummation of one equity method investment during 2016 whereby we contributed one ASC to a joint venture with a health system, which were not fully reflected in 2016 results. Additionally, in 2017, we entered into two equity method investments in which we contributed two ASCs into a joint venture with a health system. In one of these transactions, the health system contributed two additional ASCs to the joint venture.
Liquidity and Capital Resources
Our primary source of liquidity is cash flows provided by the operating activities of our subsidiaries. We and our subsidiaries also have the ability to use the ABL Facility, described below, to supplement cash flows provided by our operating activities for strategic or operating purposes. Our liquidity needs are primarily to service long-term debt and to fund working capital requirements, acquisitions and capital expenditures.
Cash and cash equivalents attributable to continuing operations at June 30, 2017 and December 31, 2016 were $441.3 million and $316.9 million, respectively. In addition, included in current assets held for sale at June 30, 2017 and December 31, 2016 are cash and cash equivalents attributable to discontinued operations of $23.3 million and $14.7 million, respectively. The table below summarizes cash flow information derived from our statements of cash flows for the six months ended June 30, 2017 and 2016 (in millions).
Six Months Ended June 30,
Net cash provided by (used in):
Operating activities. Net cash provided by operating activities for the six months ended June 30, 2017 was $378.7 million, compared to $195.0 million for the six months ended June 30, 2016. Additionally, net cash flow provided by operating activities, net of distributions to noncontrolling interests, for the six months ended June 30, 2017 was $259.7 million, compared to $79.4 million for the six months ended June 30, 2016. Cash flows from operations during the six months ended June 30, 2017 were impacted by the following:
increased operating cash flows as a result of the Merger;
payments of transaction and integration costs related to the Merger of $40.9 million;
the increase in interest payments due to the Merger-related debt refinancing; and
the timing of payments on accounts payable and certain accrued expenses, including incentive compensation based upon achieving certain performance goals for the year ended December 31, 2016. In accordance with most of our incentive plans, payments are typically made in the first six months of each fiscal year.
The principal source of our operating cash flow is the collection of accounts receivable from governmental payors, commercial payors