Substantially all of the Company’s engagements are performed under time and materials or fixed-price arrangements. For time and materials contracts, the Company utilizes the practical expedient under Accounting Standards Codification 606 – Revenue from Contracts with Customers, which states, if an entity has a right to consideration from a customer in an amount that corresponds directly with the value of the entity’s performance completed to date (for example, a service contract in which an entity bills a fixed amount for each hour of service provided), the entity may recognize revenue in the amount to which the entity has a right to invoice. The Company’s time and materials contracts are terminable and subject to postponement or delay at any time by its clients, and, as such, the performance obligations for all of the Company’s time and materials contracts have an original expected duration of one year or less. The Company recognized the following revenues from time and materials contracts:

	Three Months Ended						Nine Months Ended
	September 27, 2019			September 28, 2018			September 27, 2019			September 28, 2018
Engineering & other scientific	$	68,859		$	59,582		$	205,999		$	186,486
Environmental and health		17,803			16,755			54,612			52,987
Total time and materials revenues		86,662			76,337			260,611			239,473
Percent of total revenues		85.3	%		80.1	%		84.9	%		83.3	%

For fixed-price contracts, the Company recognizes revenue over time because of the continuous transfer of control to the customer. The customer typically controls the work in process as evidenced either by contractual termination clauses or by the Company’s rights to payment for work performed to date to deliver services that do not have an alternative use to the Company. Revenue for fixed-price contracts is recognized based on the relationship of incurred labor hours at standard rates to the Company’s estimate of the total labor hours at standard rates it expects to incur over the term of the contract. The Company believes this methodology achieves a reliable measure of the revenue from the consulting services it provides to its customers under fixed-price contracts given the nature of the consulting services the Company provides and the following additional considerations:

The Company’s fixed-price contracts are terminable and subject to postponement or delay at any time by our clients, and as such, the performance obligations for all of the Company’s fixed-price contracts have an original expected duration of one year or less. The Company recognized the following revenues from fixed price contracts:

	Three Months Ended						Nine Months Ended
	September 27, 2019			September 28, 2018			September 27, 2019			September 28, 2018
Engineering & other scientific		14,201			18,315			44,135			45,494
Environmental and health		685			650			2,339			2,413
Total fixed price revenues		14,886			18,965			46,474			47,907
Percent of total revenues		14.7	%		19.9	%		15.1	%		16.7	%

Deferred revenues represent amounts billed to clients in advance of services provided. During the third quarter of 2019, $2,452,000 of revenues were recognized that were included in the deferred revenue balance at June 28, 2019. During the first nine months of 2019, $5,144,000 of revenues were recognized that were included in the deferred revenue balance at December 28, 2018.

Reimbursements, including those related to travel and other out-of-pocket expenses, and other similar third- party costs such as the cost of materials and certain subcontracts, are included in revenues, and an equivalent amount of reimbursable expenses are included in operating expenses. Any mark-up on reimbursable expenses is included in revenues before reimbursements. The Company reports revenues net of subcontractor fees for certain subcontracts where the Company has determined that it is acting as an agent because its performance obligation is to arrange for the provision of goods or services by another party. The total amount of subcontractor fees not included in revenues because the Company was acting as an agent were $1.3 million during the third quarter of 2019. The total amount of subcontractor fees not included in revenues because the Company was acting as an agent were $11.7 million during the first nine months of 2019. The total amount of subcontractor fees not included in revenues because the Company was acting as an agent were $4.7 million during the third quarter of 2018. The total amount of subcontractor fees not included in revenues because the Company was acting as an agent were $21.9 million during the first nine months of 2018.