KYLIE JENNER, a model and reality TV star best known for being the, er, second most famous Kylie in the world, managed to cause a stir on Wall Street. With this idiosyncratic tweet

sooo does anyone else not open Snapchat any more? Or is it just me...ugh this is so sad

she knocked back the share price of Snap, the parent company of the video- and picture-sharing app. Ms Jenner’s influence in the target market is deemed to be huge; she has 24.5m Twitter followers, and her message has (at the time of writing) been retweeted 58,000 times and “liked” by 310,000. 

Snap’s share price fell 6%, reducing the company’s market value by $1.3bn. The decline was not just down to the influence of Ms Jenner, who recently gave birth to a daughter Stormi, named after the weather/porn star/grime artist. Investors were already worried about the impact of a recent app redesign. More than 1.2m people signed a petition calling for the company to withdraw the redesign, although the company showed little sign of backing down.

Do celebrity endorsements make a difference to brands? A 2012 study in the Journal of Advertising Research found that around 14%-19% of American adverts had featured such endorsements in the preceding period. It found that the support of sports stars seemed to boost the sales of products, both in absolute terms and relative to rival returns. There was a small but statistically significant boost to the share price on the day of the announcement (0.23%) and further boosts when the athlete achieved success (winning a championship or medal). 

A 2015 study by Nielsen found that celebrity endorsements have the greatest influence on Generation Z (those aged 15-20) with 16% being attracted by them, with 14% of millennials taking the same view. In contrast only 7% of boomers (aged 50-64) and 2% of those aged over 65 cared about such marketing. So it makes sense that Snapchat, a product aimed at the young, would take a hit from a celebrity like Ms Jenner, whose appeal lies with that cohort. It is the Jenner-ation gap.