pre_text: Cost of Revenue Cost of revenue increased by $15.3 million in 2018 compared to 2017. The increase was primarily due to a $7.2 million increase in employee-related costs, which includes stock-based compensation, associated with our increased headcount from 128 employees as of December 31, 2017 to 173 employees as of December 31, 2018. The remaining increase was principally the result of a $7.0 million increase in hosting, software and messaging costs, a $0.6 million increase attributed to office related expenses to support revenue generating activities and a $0.4 million increase in depreciation and amortization expense attributable to our acquired intangible assets. Gross margin percentage decreased due to our continued investment in personnel and infrastructure to support our growth in revenue.
table: Year Ended December 31, Change
table: 2018 2017 $ %
table: (dollars in thousands)
table: Cost of revenue $ 46,810 $ 31,503 $ 15,307 48.6%
table: Gross margin % 68% 70%
question: Analyse this data from a financial earnings document. What is the change in the gross margin between 2018 and 2019?