Salmon, 42, is a psychology professor at the University of Redlands in Redlands, Calif., and the author of "The Power of Middle Children," a book about the traits exhibited by those who fall in the center of the sibling order.
Salmon, who grew up as her family's youngest child, said she wrote the book "to dispel the idea that middles are resentful and angry."
Being a middle child, she argues, can have great benefits in the areas of independence, stable relationships and job satisfaction.
Using her own research as well as that of others, Salmon argues that middle-born children often make the best leaders, diplomats and marital partners.
"To me, the things that are most important is that middle-borns have these great negotiating skills and they're innovators," Salmon said. "Their ability to think outside the box is something I'd like people to recognize."
One of the examples she likes to use is Bill Gates.
"Everyone assumes he's a first-born," she said. "His older sister is an accountant and fits very well with what a first-born is supposed to be."
Bill Gates, she said, not only exhibits the leadership and innovative skills that middle-born children often excel in, but his philanthropic efforts fit within the group's traits.
Middle-born children, Salmon said, often show a heightened degree of empathy. "They're more likely to work for nonprofits. (In surveys) middle-borns made less money but were more satisfied with their jobs."
Other famous middle-born children she likes to cite include George Washington, Abraham Lincoln and Nelson Mandella.
During her eight years at the University of Redlands, Salmon has published other books, but they were aimed at an academic audience. This is her first book written for a wide audience and her agent suggested she get some assistance in the writing process from another author.
Katrin Schumann, a Boston-based writer who had already co-authored a book on parenting. Salmon said Schumann was involved in collecting data in one study, but primarily helped in the writing of the book.
Salmon has no children. Schumann has three.
"She sees a lot of what we talked about in her daughter," Salmon said of her co-author.
Smaller family sizes have led to a downward trend in the number of middle-born children. Salmon said there are 70 million middle-born children and adults in the country.
"We think that's a concern," Salmon said of the decline. Middle-born children "are justice seekers, for example. It's a problem to have that trending down."
But don't blame middle-born children.
"Middles seem more likely to have more children themselves," she said. "They like the feeling of community."
She said research has shown that middle-born children may also be better partners when it comes to relationships. In a survey she conducted among adults, mostly in their 20s, between 4 percent and 5 percent of middle-born respondents reported cheating while in a monogamous relationship. The rate among first-born children was 25 percent.
At the same time, she said, they may be more adventurous within their relationships.
"One study showed they were less judgmental on sexual behavior," she said. "The Israelis did a study on marital satisfaction and found middle-borns had more satisfaction. (Researchers) said middle-borns are like type-O blood donors. They go well with any other type. One of the things they're really good at is compromise."
Salmon wants her colleagues to take middle-born children more seriously as subjects.
"One of the messages for researchers is, you should do your research by breaking up first-, middle- and last-born," she said. Traditionally, studies have typically broken siblings into two categories, first-born and others.
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