That's a stupid conclusion by the surveyors. If 10% don't tip, then 90% are tipping.
This is surveyor bias as well..
People who DO tip will say yes,
People who Know they should tip will say yes, and lie about it,
People who don't tip and admit it? That's a rare segment of the population.
(A better way to collect this is to survey waitresses and bartenders)
10% ADMIT they don't tip. The important assumption to make is ADMIT.
Human psychology tells me that people who don't tip, YET KNOW THE SHOULD, will lie about it.
A survey like this will result in a lower number of people admitting they don't tip then those who actually don't tip.
And it is statistically relevant, that means that 3 times as many millennials don't tip compared to the rest. The %s they tip are also probably lower as well.
Uber/lyft on the other hand? That's a situation of people not thinking you need to tip an uber driver.