Dx attributes revenues to a geographical region based upon where the diagnostic test is performed, while DD attributes revenues to a geographical region based upon where the services are performed. The Company's revenue by segment payers/customer groups for the years ended December 31, 2021, 2020 and 2019 is as follows:


	Year Ended December 31, 2021				For the Year Ended December 31, 2020											For the Year Ended December 31, 2019
	North America		Europe			Other		Total		North America		Europe		Other			Total		North America		Europe		Other		Total
Payer/Customer
Dx
Clients	17	%	—	%		—	%	17	%	20	%	—	%	—	%		20	%	17	%	—	%	—	%	17	%
Patients	6	%	—	%		—	%	6	%	6	%	—	%	—	%		6	%	8	%	—	%	—	%	8	%
Medicare and Medicaid	7	%	—	%		—	%	7	%	7	%	—	%	—	%		7	%	8	%	—	%	—	%	8	%
Third party	34	%	—	%		—	%	34	%	32	%	—	%	—	%		32	%	27	%	—	%	—	%	27	%
Total Dx revenues by payer	64	%	—	%		—	%	64	%	65	%	—	%	—	%		65	%	60	%	—	%	—	%	60	%

DD
Pharmaceutical, biotechnology and medical device companies	17	%	13	%		6	%	36	%	17	%	11	%	7	%		35	%	21	%	12	%	7	%	40	%

Total revenues	81	%	13	%		6	%	100	%	82	%	11	%	7	%		100	%	81	%	12	%	7	%	100	%

Dx is an independent clinical laboratory business. It offers a comprehensive menu of frequently requested and specialty diagnostic tests through an integrated network of primary and specialty laboratories across the U.S. In addition to diagnostic testing along with occupational and wellness testing for employers and forensic DNA analysis, Dx also offered a range of other testing services.

Within the Dx segment, a revenue transaction is initiated when Dx receives a requisition order to perform a diagnostic test. The information provided on the requisition form is used to determine the party that will be billed for the testing performed and the expected reimbursement. Dx recognizes revenue and satisfies its performance obligation for services rendered when the testing process is complete and the associated results are reported. Revenues are distributed among four payer portfolios - clients, patients, Medicare and Medicaid and third party. Dx considers negotiated discounts and anticipated adjustments, including historical collection experience for the payer portfolio, when revenues are recorded.

Client payers represent the portion of Dx’s revenue related to physicians, hospitals, health systems, accountable care organizations (ACOs), employers and other entities where payment is received exclusively from the entity ordering the testing service. Generally, client sales are recorded on a fee-for-service basis at Dx’s client list price, less any negotiated discount. A portion of client billing is for laboratory management services, collection kits and other non-testing services or products. In these cases, revenue is recognized when services are rendered or delivered.

This portfolio includes revenue from uninsured patients and member cost-share for insured patients (e.g., coinsurance, deductibles and non-covered services). Uninsured patients are billed based upon Dx’s patient list fee schedules, net of any discounts negotiated with physicians on behalf of their patients. Dx bills insured patients as directed by their health plan and after consideration of the fees and terms associated with an established health plan contract.

This portfolio relates to fee-for-service revenue from traditional Medicare and Medicaid programs. Revenue from these programs is based on the fee schedule established by the related government authority. In addition to contractual discounts, other adjustments including anticipated payer denials are considered when determining revenue. Any remaining adjustments to revenue are recorded at the time of final collection and settlement. These adjustments are not material to Dx’s results of operations in any period presented.

Third party includes revenue related to MCOs. The majority of Dx's third-party revenue is reimbursed on a fee-for-service basis. These payers are billed at Dx's established list price and revenue is recorded net of contractual discounts. The majority of Dx’s MCO sales are recorded based upon contractually negotiated fee schedules with sales for non-contracted MCOs recorded based on historical reimbursement experience.

In addition to contractual discounts, other adjustments including anticipated payer denials are considered when determining revenue. Any remaining adjustments to revenue are recorded at the time of final collection and settlement. These adjustments are not material to Dx’s results of operations in any period presented.

Third-party reimbursement is also received through capitation agreements with MCOs and independent physician associations (IPAs). Under capitated agreements, revenue is recognized based on a negotiated per-member, per-month payment for an agreed upon menu of tests, or based upon the proportionate share earned by Dx from a capitation pool. When the agreed upon reimbursement is based solely on an established rate per member, revenue is not impacted by the volume of testing performed. Under a capitation pool arrangement, the aggregate value of an established rate per member is distributed based on the volume and complexity of the procedures performed by laboratories participating in the agreement. Dx recognizes revenue monthly, based upon the established capitation rate or anticipated distribution from a capitated pool.

DD is a CRO business that provides end-to-end drug development services. DD provides these services predominantly to pharmaceutical, biotechnology and medical device companies worldwide. A majority of DD’s revenues are earned under contracts that range in duration from a few months to several years. These contracts generally take the form of fee-for-service or fixed-price arrangements subject to pricing adjustments based on changes in scope. The total contract value is estimated at the beginning of the contract, and is equal to the amount expected to be billed to the customer. Other payments and billing adjustments may also factor into the calculation of the total contract value, such as the reimbursement of out-of-pocket costs and volume-based rebates.

The majority of DD's contracts contain a single performance obligation. For contracts that include multiple performance obligations, DD allocates the contract value to the goods and services based on a customer price list, if available. If a price list is not available, DD will estimate the transaction price using either market prices or an “expected cost plus margin” approach.

Fee-for-service contracts are typically priced based on transaction volume or time and materials. For volume based contracts the contract value is entirely variable and revenue is recognized as the specific product or service is completed. For services billed based on time and materials, revenue is recognized using the right to invoice practical expedient.

Fixed-price contracts are typically recognized as revenue over time based on a proportional-performance basis, using either input or output methods that are specific to the service provided. In an output method, revenue is determined by dividing the actual units of output achieved by the total units of output required under the contract and multiplying that percentage by the

total contract value. When using an input method, revenue is recognized by dividing the actual units of input incurred by the total units of input budgeted in the contract, and multiplying that percentage by the total contract value. The estimate of total units of input at completion requires significant judgment and the estimates are based on various assumptions of events that often span several years. These estimates are reviewed periodically and any adjustments are recognized on a cumulative catch-up basis in the period they become known.

Contracts are often modified to account for changes in contract specifications and requirements. Generally, when contract modifications create new performance obligations, the modification is considered to be a separate contract and revenue is recognized prospectively. When contract modifications change existing performance obligations, the impact on the existing transaction price and measure of progress for the performance obligation to which it relates is generally recognized as an adjustment to revenue (either as an increase in or a reduction of revenue) on a cumulative catch-up basis.

Most contracts are terminable with or without cause by the customer, either immediately or upon notice. These contracts often require payment to DD of expenses to wind-down the study or project, fees earned to date and, in some cases, a termination fee or a payment to DD of some portion of the fees or profits that could have been earned by DD under the contract if it had not been terminated early. Termination fees are included in revenues when services are performed and realization is assured.

DD incurs sales commissions in the process of obtaining contracts with customers, which are recoverable through the service fees in the contract. Sales commissions that are payable upon contract award are recognized as assets and amortized over the expected contract term, along with related payroll tax expense. The amortization of commission expense is based on the weighted average contract duration for all commissionable awards in the respective business in which the commission expense is paid, which approximates the period over which goods and services are transferred to the customer. The amortization period of sales commissions ranges from approximately 1-5 years, depending on the business. For businesses that enter primarily short-term contracts, the Company applies the practical expedient which allows costs to obtain a contract to be expensed when incurred if the amortization period of the assets that would otherwise have been recognized is one year or less. Amortization of assets from sales commissions is included in selling, general, and administrative expense.

DD incurs costs to fulfill contracts with customers, which are recoverable through the service fees in the contract. Contract fulfillment costs include software implementation costs and setup costs for certain services. These costs are recognized as assets and amortized over the expected term of the contract to which the implementation relates, which is the period over which services are expected to be provided to the customer. This period typically ranges from 2-5 years. Amortization of deferred contract fulfillment costs is included in cost of goods sold.

Amortization related to sales commission assets and associated payroll taxes for the years ended December 31, 2021, 2020, and 2019 was $27.5, $23.2 and $21.2, respectively. Amortization related to deferred contract fulfillment costs for the years ended December 31, 2021, 2020 and 2019 was $14.2, $10.1 and $8.7, respectively. Impairment expense related to contract costs was immaterial to the Company’s consolidated statement of operations. The Company applies the practical expedient to not recognize the effect of financing in its contracts with customers, when the difference in timing of payment and performance is one year or less.

Differences in the timing of revenue recognition and associated billing and cash collections result in recording accounts receivable, unbilled services and unearned revenue in the consolidated balance sheet. Payments received in advance of services being provided are contract liabilities recognized as unearned revenue. Revenue recognized in advance of billing are recognized as unbilled services and the majority of our unbilled services represent unbilled receivables. Once a customer is invoiced, the contract asset is reduced for the amount billed, and a corresponding accounts receivable is recognized. All contract assets are billable to customers within one year from the respective balance sheet date. The following table provides information about accounts receivables, unbilled services, and unearned revenue from contracts with customers:


	December 31, 2021		December 31, 2020
Dx accounts receivable	$	1,193.8	$	1,515.5
DD accounts receivable	1,089.2		986.4
Less DD allowance for doubtful accounts	(21.5)		(22.1)
Accounts receivable	$	2,261.5	$	2,479.8

Gross unbilled services	$	730.8	$	548.1
Less reserve for unbilled services	(14.0)		(11.3)
Unbilled services	$	716.8	$	536.8

Unearned revenue	$	558.5	$	506.5

Revenue recognized during the period, that was included in the unearned revenue balance at the beginning of the period, for the years ended December 31, 2021, 2020, and 2019 was $319.4, $262.6, and 250.2, respectively.

With the adoption of the current expected credit loss standard in 2020, the Company estimates future expected losses on accounts receivable, unbilled services and notes receivable over the remaining collection period of the instrument. The rollforward for the allowance for credit losses for the year ended December 31, 2021, is as follows:


	Accounts Receivable		Unbilled Services		Note and Other Receivables		Total
Allowance for credit losses as of December 31, 2019	$	19.0	$	2.3	$	—	$	21.3
Current expected credit losses opening balance impact on retained earnings	1.8		0.2		5.0		7.0
Credit loss expense	7.0		9.0		0.7		16.7
Write offs	(5.7)		(0.2)		—		(5.9)
Allowance for credit losses as of December 31, 2020	$	22.1	$	11.3	$	5.7	$	39.1

Credit loss expense	3.8		2.7		(5.0)		1.5
Write offs	(4.4)		(0.1)		—		(4.5)
Ending allowance for credit losses	$	21.5	$	13.9	$	0.7	$	36.1

Long-term contracts at the Company consist primarily of fully managed clinical studies within the DD segment. The amount of existing performance obligations under such long-term contracts unsatisfied as of December 31, 2021, and 2020, was $5,757.5 and $5,128.4, respectively. The Company expects to recognize approximately 40.0% of the remaining performance obligations as of December 31, 2021, as revenue over the next 12 months, and the balance thereafter. The Company's long-term contracts generally range from 1 to 8 years.

The Company applied the practical expedient and does not disclose information about remaining performance obligations that have original expected durations of one year or less. The Company also did not disclose information about remaining performance obligations when the variable consideration was related to a wholly unsatisfied performance obligation within a series of obligations.

Within DD, revenue of $69.8 and $80.9 was recognized during the year ended December 31, 2021, and December 31, 2020, respectively, from performance obligations that were satisfied in previous periods. This revenue comes primarily from adjustments related to changes in scope, and to a lesser extent changes in estimates in full service clinical studies.