Tipping leads to an increased risk of sexism and harassment towards waitresses, a new study has revealed. 

Customers create a “power imbalance” when leaving tips for restaurant staff which can remove diners’ inhibition in making unwanted sexual advances and lewd comments, researchers suggested. 

The team from Pennsylvania State University, whose findings are published in the Journal of Applied Psychology, conducted two experiments to examine how tipping can lead to a spike in sexual harassment.

In the first trial they recruited 92 participants who worked at least 35 hours a week at a job where they regularly received tips from customers.

They were questioned on their financial dependence on tips, how often they were asked to project a positive attitude towards customers and  the number of times they had been sexually harassed at work over the past six months. 

After analysing the data of the first study, researchers found that when employees reported a greater dependency on customers’ tips they experienced more cases of sexual harassment.

But only when employees were also required to be friendly at all times. 

The “service with a smile” approach, which waiting staff are often forced to adopt by their managers, may have encouraged the customers to feel a greater sense of entitlement in interactions. 

Higher hourly wages from employers and less financial dependence on tips, may also help to reduce cases of sexual harassment, academics said. 

Alicia Grandey, liberal arts professor of psychology at Pennsylvania State University and author of the study, said: "It may not be necessary to completely eliminate customer tips.

"But rather reduce the dependence on tips by offering a livable wage.

She added: "Based on our results, if employees were less dependent on customer tips, harassment would be less likely to occur because customers would hold less power over the employee."

For the second study, the team recruited 229 men to participate in an online experiment.

They were randomly assigned to one of four study conditions in which a visit to a restaurant was simulated.

In the first setting, the waitress appeared smiley and needed tips. For the second they were friendly but not financially dependent on tips. 

In the third they acted neutral and reliant on tips and in the fourth neutral again and not dependent on tips.

The participants then answered questions about the service interaction.

The results – even though it took place from the customers’ point of view – echoed the findings from the first study.

"Customers may not be thinking about how the employee depends on their tips for income, until they see that smile as an expression of deference, which suggests a low likelihood that they will resist or report unwanted advances," Prof Grandey said.

Timothy Kundro, an assistant professor of management and organisation at the University of Notre Dame, said: "Previous research has suggested that service employees are some of the most likely to face sexual harassment, and particularly from customers.

"We were interested in understanding why sexual harassment is so pervasive in this context, and curious if any of these insights could provide actionable insights for organisations."

He suggested bosses reduce workers’ reliance on tips, or relax expectations for smiling at customers even when their behavior becomes inappropriate.