Table:
|  |  | Year Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
|  |  | (In millions) |  |
| Operating income | $1,203 | $1,400 | $1,005 |
| As percentage of net revenues | 12.6% | 14.5% | 12.0% |
Paragraphs:
Operating income in 2019 was $1,203 million, decreasing by $197 million compared to 2018, reflecting normal price pressure, increased unsaturation charges and higher R&D spending, partially offset by higher level of grants and favorable currency effects, net of hedging.
Operating income in 2018 was $1,400 million, improved by $395 million compared to 2017, reflecting higher volumes, improved manufacturing efficiencies and product mix and lower restructuring charges, partially offset by unfavorable currency effects, net of hedging, normal price pressure and higher operating expenses.
Question:
What did the improved operating income in 2018 indicate?
Answer: reflecting higher volumes, improved manufacturing efficiencies and product mix and lower restructuring charges, partially offset by unfavorable currency effects, net of hedging, normal price pressure and higher operating expenses.