NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (continued)
d) Accounts Receivable and Allowance for Doubtful Accounts
Healthcare accounts receivable is recorded at the time Healthcare segment revenue is recognized and is presented on the consolidated balance sheet net of an allowance for doubtful accounts. The percentages and amounts used to record bad debt expense and the allowance for doubtful accounts are supported by various methods and analyses, including current and historical cash collections and the aging of receivables by payor. Because of continuing changes in the health care industry and third-party reimbursement, it is possible that our estimates of collectability could change, which could have a material impact on our operations and cash flows.
Other accounts receivable is related to the Research segment and Corporate and Other category and is recorded at the time revenue is recognized, when products are shipped or services are performed. We estimate an allowance for doubtful accounts on a specific account basis, and consider several factors in our analysis including customer specific information and the aging of the account.
We write off receivables when the likelihood for collection is remote and when we believe collection efforts have been fully exhausted and we do not intend to devote additional resources in attempting to collect. We perform write-offs on a monthly basis.
e) Concentrations of Credit Risk
Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash, cash equivalents, Healthcare accounts receivable and other accounts receivable. We maintain our cash and cash equivalents with high quality financial institutions to mitigate this risk. We perform ongoing credit evaluations of our customers and generally do not require collateral. We record an allowance for doubtful accounts in accordance with the procedures described above. Past-due amounts are written off against the allowance for doubtful accounts when collections are believed to be unlikely and all collection efforts have ceased.
At September 30, 2018 and December 31, 2017, one payor, Medicare, accounted for 16% and 21%, respectively, of our gross accounts receivable.
f) Noncontrolling Interest
The consolidated financial statements reflect the application of Accounting Standards Codification (“ASC”) 810 - Consolidations, which establishes accounting and reporting standards that require: (i) the ownership interest in subsidiaries held by parties other than the parent to be clearly identified and presented in the consolidated balance sheet within stockholders’ equity, but separate from the parent’s equity; (ii) the amount of consolidated net income/(loss) attributable to the parent and the noncontrolling interest to be clearly identified and presented in the consolidated statements of operations; and (iii) changes in a parent’s ownership interest while the parent retains its controlling financial interest in its subsidiary to be accounted for consistently.
g) Stock-Based Compensation
ASC 718, Compensation—Stock Compensation (“ASC 718”), addresses the accounting for share-based payment transactions in which an enterprise receives employee services in exchange for: (i) equity instruments of the enterprise or (ii) liabilities that are based on the fair value of the enterprise’s equity instruments or that may be settled by the issuance of such equity instruments. ASC 718 requires that an entity measure the cost of equity-based service awards issued to employees, such as stock options and