Contract Estimates Use of the cost-to-cost or other similar methods of revenue recognition requires us to make reasonably dependable estimates regarding the revenue and cost associated with the design, manufacture and delivery of our products and services. Revisions or adjustments to estimates of the transaction price, estimated costs at completion and estimated profit or loss of a performance obligation are often required as work progresses under a contract, as experience is gained, as facts and circumstances change and as new information is obtained, even though the scope of work required under the contract may not change. In determining the estimated costs at completion, we have to make assumptions regarding labor productivity and availability, the complexity of the work to be performed, the availability of materials, estimated increases in wages and prices for materials, performance by our subcontractors, and the availability and timing of funding from our customer, among other variables. Revisions or adjustments to our estimated transaction price and estimated costs at completion may also be required if contract modifications occur. The revisions in contract estimates, if significant, can materially affect our results of operations and cash flows, and in some cases result in liabilities to complete contracts in a loss position. Based upon our history, we believe we have the ability to make reasonable estimates for these items. We have accounting policies and controls in place to address these, as well as other contractual and business arrangements to properly account for long-term contracts, and we continue to monitor and improve such policies, controls, and arrangements. For other information on such policies, controls and arrangements, see our discussion in Item 9A of this Form 10-K. Products and services provided under long-term, fixed-price contracts represented approximately 97% of our sales for 2019. Because of the significance of the judgments and estimation processes, it is likely that materially different amounts could be recorded if we used different assumptions or if our underlying circumstances were to change. For example, if underlying assumptions were to change such that our estimated profit rate at completion for all fixed-price contracts accounted for under the cost-to-cost percentage-of-completion method was higher or lower by one percentage point, our 2019 operating income would have increased or decreased by approximately $6.5 million. When adjustments in estimated contract revenues or estimated costs at completion are required, any changes from prior estimates are recognized by recording adjustments in the current period for the inception-to-date effect of the changes on current and prior periods using the cumulative catch-up method of accounting. When estimates of total costs to be incurred on a contract exceed total estimates of revenue to be earned, a provision for the entire loss on the contract is recorded in the period the loss is determined. The aggregate impact of net changes in contract estimates are presented in the table below (amounts in thousands). For other information on accounting policies we have in place for recognizing sales and profits and the impact of our adoption of ASC 606, see our discussion under “Revenue Recognition” in Note 1 to the Consolidated Financial Statements.

Years Ended September 30,

2019	2018	2017

Operating income (loss)	$ (2,235)	$ (6,986)	$ 5,737

Net income (loss) from continuing operations	(2,351)	(5,146)	3,208

Diluted earnings per share	(0.08)	(0.19)	0.12

Question: For which periods is the aggregate impact of net changes in contract estimates presented in the table?
Answer: 2019; 2018; 2017