4. Accounts Receivable, Net of Allowance for Doubtful Accounts

Our receivables, which are recorded when services are performed or when services are billed in advance, are claims against third parties that will generally be settled in cash. The carrying value of our receivables, net of the allowance for doubtful accounts, represents the estimated net realizable value. We estimate our allowance for doubtful accounts based on consideration of a number of factors, including the length of time trade accounts are past due, our previous loss history, the creditworthiness of individual customers, economic conditions affecting specific customer industries, and economic conditions in general. We write off past-due receivable balances after all reasonable collection efforts have been exhausted. We credit payments subsequently received on such receivables to the allowance for doubtful accounts in the period we receive the payment. We record delinquent finance charges on outstanding accounts receivable only if they are collected.