Table:
|  | Three Months Ended | Three Months Ended | Three Months Ended | % Variation | % Variation |
| --- | --- | --- | --- | --- | --- |
|  | December 31, 2019 | September 29, 2019 | December 31, 2018 | Sequential | Year- Over- Year |
|  | (Unaudited, in millions) |  |  |  |  |
| Net sales | $ 2,750 | $ 2,547 | $ 2,633 | 8.0% | 4.5% |
| Other revenues | 4 | 6 | 15 | (45.0) | (77.4) |
| Net revenues | $ 2,754 | $ 2,553 | $ 2,648 | 7.9% | 4.0% |
Paragraphs:
Our fourth quarter 2019 net revenues amounted to $2,754 million, registering a sequential increase of 7.9%, 290 basis points above the mid-point of our guidance, with all product groups contributing to the growth. The sequential increase resulted from higher volumes of approximately 7% and an increase of approximately 1% in average selling prices, the latter entirely due to product mix, while selling prices remained substantially stable.
On a year-over-year basis, our net revenues increased by 4.0%. This increase was entirely due to an increase of approximately 6% in average selling prices, partially offset by an approximate 2% decrease in volumes. The average selling prices increase was entirely driven by improved product mix of approximately 9%, partially offset by lower selling prices of approximately 3%.
Question:
What led to increase in average selling price on a year-over-year basis?
Answer: driven by improved product mix of approximately 9%, partially offset by lower selling prices of approximately 3%.