pre_text: Research and development Research and development expense consists primarily of salaries and other personnel-related costs; the cost of products, materials, and outside services used in our R&D activities; and depreciation and amortization expense associated with R&D specific facilities and equipment. We maintain a number of programs and activities to improve our technology and processes in order to enhance the performance and reduce the costs of our solar modules. The following table shows research and development expense for the years ended December 31, 2019, 2018, and 2017: Research and development expense in 2019 increased compared to 2018 primarily due to increased material and module testing costs and higher employee compensation expense.
table: Year Ended Change
table: (Dollars in thousands) 2019 2018 2017 2019 over 2018 2018 over 2017
table: Research and development $96,611 $84,472 $88,573 $12,139 14% $(4,101) (5)%
table: % of net sales . 3.2% 3.8% 3.0%
question: Analyse this data from a financial earnings document. What is the difference in net sales amount between 2018 and 2017?