As with nearly any kind of study, there are many similar ones with opposite results that makes you kind of realize the whole world can't be explained through surveys and studies only.

Mapping the scale of the narcissism epidemic: Increases in narcissism 2002–2007 within ethnic groups - https://www.sciencedirect.com/science/article/pii/S009265660...

Egos Inflating Over Time: A Cross-Temporal Meta-Analysis of the Narcissistic Personality Inventory - http://onlinelibrary.wiley.com/doi/10.1111/j.1467-6494.2008....

And then there are those who question whether the Narcissistic Personality Inventory is even a good measure of narcissism at all

Addressing criticisms of the Narcissistic Personality Inventory (NPI). - http://psycnet.apa.org/record/2011-16529-013