The next time you encounter discriminatory treatment in a restaurant, take a minute to protect the jobs of the people who work there: Take your complaint to a manager.

A recent survey published by the Cornell Hospitality Quarterly has found satisfied customers are a key to a successful restaurant; and poor customer service hurts sales. The research by Sachin Gupta, Edward McLaughlin, and Miguel Gomez, analyzed the performance of three restaurant chains and established a connection between customer satisfaction (as measured by intention to return) and increased sales. In plain talk, satisfied customers tend to come back and buy more stuff.

According the authors,  a 1-percent increase in customers’ likelihood of returning could amount to as much as $1.3 million in extra sales (even though the daily increase in sales from satisfied customers is small).

Four factors drove consumer satisfaction levels:  delicious food, appropriate cost, a cheerful greeting, and attentive service.

Earlier this year, the Tri-State Defender did a ground-breaking series on restaurant tipping trends and research. In subsequent online and street surveys, some readers reported they sometimes receive lesser quality service from wait staff who assumed they don’t tip because they are African American.

“If unhappy customers leads to lower sales, then it stands to reason that discriminatory actions by wait staff may lead to lower sales as well,” said Linda S. Wallace, a columnist who wrote the Defender’s series.

“This is a wake up call for restaurants. I find find customers who are discriminated against tend to be very unhappy.”

Wallace said many major restaurants now randomly select customers to survey regarding the service.

“The chains are beginning to listen to and respond to African Americans’ complaints of discriminatory service levels,” she said.

“About two years ago, I reported a waitress who had basically ignored my table while I was hosting a business lunch. The next week, the chain sent a regional manager from Washington to meet with the local manager and waitress. The chain sent me an apology and $50 in gift cards, which I donated to my favorite charities.”

Cornell University says the study employs a series of mathematical models to make its prediction regarding how the level of customer satisfaction affects the likelihood that they will come back. Those “come-back” scores and other variables affect restaurant performance, as measured by sales and entrée counts.