Unallocated Amounts
In determining revenue, gross profit and income from operations for our segments, we do not include in revenue the amortization of acquisition related deferred revenue adjustments, which reflect the fair value adjustments to deferred revenues acquired in a business acquisition. We also exclude the amortization of intangible assets, stock-based compensation expense, expenses not reflective of our core business and transaction-related costs and non-cash asset impairment charges from the operating segment data provided to our Chief Operating Decision Maker.
Expenses not reflective of our core business relate to certain severance, product consolidation, legal, consulting and other charges. Accordingly, these amounts are not included in our reportable segment results and are included in the “Unallocated Amounts” category.
The “Unallocated Amounts” category also includes (i) corporate general and administrative expenses (including marketing expenses) and certain research and development expenses related to common solutions and resources that benefit all of our business units, all of which are centrally managed, and (ii) revenue and the associated cost from the resale of certain ancillary products, primarily hardware.
Year Ended December 31, 2019 Compared with the Year Ended December 31, 2018
Revenue from the resale of ancillary products, primarily consisting of hardware, is customer- and project-driven and, as a result, can fluctuate from period to period. The increase in revenue for the year ended December 31, 2019 compared to the prior year was primarily due to only $2 million in amortization of acquisition-related deferred revenue adjustments being recorded during 2019, compared to $24.3 million during 2018.
Gross unallocated expenses, which represent the unallocated loss from operations excluding the impact of revenue, totaled $478 million for the year ended December 31, 2019 compared to $533 million for the year ended December 31, 2018. The decrease was primarily the result of (i) lower asset impairment and goodwill charges of $35 million, (ii) lower net transaction-related severance and legal expenses of $16 million and (iii) lower acquisition related amortization of $1 million. These were partially offset with $3 million in additional stock-based compensation expense.
Year Ended December 31, 2018 Compared with the Year Ended December 31, 2017
Revenue from the resale of ancillary products, primarily consisting of hardware, is customer and project driven and, as a result, can fluctuate from period to period. Revenue for the year ended December 31, 2018 compared with the prior year improved primarily due to lower recognition of amortization of acquisition-related deferred revenue adjustments, which reflect the fair value adjustments to deferred revenues acquired in the EIS Business, Practice Fusion, Health Grid and NantHealth provider/patient engagement acquisitions.
Such adjustments totaled $24 million for the year ended December 31, 2018 compared with $29 million for the year ended December 31, 2017.
Gross unallocated expenses, which represent the unallocated loss from operations excluding the impact of revenue, totaled $533 million for the year ended December 31, 2018 compared with $424 million for the prior year. The increase in the year ended December 31, 2018 compared with prior year was primarily driven by higher transaction-related, severance and legal expenses, primarily related to the acquisitions of the EIS Business, Practice Fusion and Health Grid,
which included higher (i) asset impairment charges of $58 million, (ii) goodwill impairment charges of $14 million, (iii) transaction-related, severance and legal expenses of $30 million, and (iv) amortization of intangible and acquisition-related asset of $9 million. The increase in amortization expense was primarily due to additional amortization expense associated with intangible assets acquired as part of business acquisitions completed since the third quarter of 2017.
Table:
 |  |  | Year Ended December 31, |  | 
(In thousands) | 2019 | 2018 | 2017 | 2019 % Change from 2018 | 2018 % Change from 2017
Revenue | $13,346 | $(6,386) | $(13,383) | NM | (52.3%)
Gross profit | $(63,522) | $(86,228) | $(85,130) | (26.3%) | 1.3%
Gross margin % | NM | NM | NM |  | 
Loss from operations | $(465,176) | $(539,237) | $(437,431) | (13.7%) | 23.3%
Operating margin % | NM | NM | NM |  | 


Question: What led to increase in revenue for the year ended December 31, 2019 compared to the prior year?
Answer: due to only $2 million in amortization of acquisition-related deferred revenue adjustments being recorded during 2019, compared to $24.3 million during 2018.