Table:
|  | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, | Variation | Variation |
| --- | --- | --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 | 2019 vs 2018 | 2018 vs 2017 |
|  | (In millions) | (In millions) | (In millions) |  |  |
| Selling, general and administrative expenses | $(1,093) | $(1,095) | $(981) | 0.3% | (11.7)% |
| Research and development expenses | (1,498) | (1,398) | (1,296) | (7.1) | (7.9) |
| Total operating expenses | $(2,591) | $(2,493) | $(2,277) | (3.9)% | (9.5)% |
| As percentage of net revenues | (27.1)% | (25.8)% | (27.3)% | -130 bps | +150 bps |
Paragraphs:
The 2019 operating expenses increased 3.9% compared to the prior year, mainly due to salary dynamic, increased spending in certain R&D programs and higher share-based compensation cost, partially offset by favorable currency effects, net of hedging.
The 2018 operating expenses increased 9.5% compared to the prior year, mainly due to unfavorable currency effects, net of hedging, salary dynamic, increased R&D activities and higher costs of the share-based compensation plans.
The R&D expenses were net of research tax credits in France and Italy, which amounted to $126 million in 2019, $138 million in 2018 and $124 million in 2017.
Question:
In 2018, what were the reasons for increase in operating expenses?
Answer: due to unfavorable currency effects, net of hedging, salary dynamic, increased R&D activities and higher costs of the share-based compensation plans.