Table:
|  | Year Ended December 31, |  | Change |  |
| --- | --- | --- | --- | --- |
|  | 2019 | 2018 | $ | % |
|  |  | (dollars in thousands) |  |  |
| Research and development | $ 50,024 | $ 41,305 | $ 8,719 | 21.1% |
| % of revenue | 25% | 28% |  |  |
Paragraphs:
Research and Development Expense
Research and development expense increased by $8.7 million in 2019 compared to 2018. The increase was primarily due to a $5.4 million increase in employee-related costs, which includes stock-based compensation, associated with our increased headcount from 229 employees as of December 31, 2018 to 252 employees as of December 31, 2019, a $1.3 million increase in hosting and software related cost to support research and development activities and an increase of $0.4 million in office related expenses to support research and development activities. In addition, a total of $6.5 million of internally-developed software costs during 2019 and $7.7 million of internally-developed software costs during 2018 were capitalized, resulting in an increase of the expense by $1.2 million compared to 2018.
Question:
What was the average Research and development expense for 2018 and 2019?