We recognize revenue from our packaging and test services, net of value-added or other similar taxes, when there is evidence of an arrangement, delivery has occurred or services have been rendered, fees are fixed or determinable and collectibility is reasonably assured. Generally these criteria are met and revenue is recognized upon shipment. If the revenue recognition criteria are not met, we defer the revenue. Deferred revenue generally results from two types of transactions: contractual invoicing at interim points in the packaging and test process prior to shipment of the finished product and customer advances for supply agreements with customers where we commit capacity in exchange for customer prepayment of services. These prepayments are deferred and recorded as customer advances within accrued expenses and other non-current liabilities. We generally do not take ownership of customer-supplied semiconductor wafers. Title and risk of loss remains with the customer for these materials at all times. Accordingly, the cost of the customer-supplied materials is not included in our Consolidated Financial Statements. An allowance for sales credits is recorded as a reduction to sales and accounts receivable during the period of sale such that accounts receivable is reported at its estimated net realizable value. The allowance for sales credits is an estimate of the future credits we will issue for billing adjustments primarily for invoicing corrections and miscellaneous customer claims and is estimated based upon recent credit issuance, historical experience and specific identification of known or expected sales credits at the end of the reporting period. Additionally, provisions are made for doubtful accounts when there is doubt as to the collectibility of accounts receivable. The allowance for doubtful accounts is recorded as bad debt expense and is classified as selling, general and administrative expense. The allowance for doubtful accounts is based upon specific identification of doubtful accounts considering th