Cab tipping culture is totally different and I would imagine varies significantly locally.

This is the study I was recalling: https://www.academia.edu/51293325/Restaurant_Tipping_and_Ser...

Though in looking for that I did find this other study that found racial bias: https://onlinelibrary.wiley.com/doi/abs/10.1111/soin.12056

FWIW it comes off as pretty snarky to provide evidence and then pre-emptively insult the reader by assuming they won’t respond to it, or assume that disagreement will be a result of rejecting evidence in general and not having some more specific objection (e.g., cab vs restaurant tipping culture being different)