THE first-born child is closest to a mother's heart, and the youngest is spoiled - if you believe anecdotal evidence.

But numerous studies on birth order mean parents no longer have to rely on anecdotes to assess whether being eldest or youngest affects their children. Academics are constantly pursuing the truth about how birth order can make a difference to characteristics and parental treatment, and in the latest rash of studies intelligence, personality, discipline, time and attention have all been assessed.

Scientists at Vrije University in Amsterdam have found that the oldest child is more likely to have a higher IQ, and the youngest likely to have the lowest. It's not known why this is the case, although it may be related to the extra attention first-born children get from their parents, at least until another sibling is born.

Certainly, research from Brigham Young University in the USA found that first-born children get about 3,000 more hours of quality time with their parents between the ages of four and 13 than the next sibling gets within the same age range.

"We've known for a long time that eldest children have better outcomes and these findings on quality time provide one explanation why," says economics professor Joseph Price, who led the study.

"If your goal as a parent is to equalize outcomes across your children, you should be aware of this natural pattern and try to give younger children more quality time," adds Price.

But another study, at the University of California, found that parents' most favoured child tends to be the last-born. It also concluded that last-borns are warm, sociable, extrovert and creative, but questioning of authority.

Middle-borns are said to be rebellious, impulsive and open to new experiences. They perform worse at school, and are often the peacemakers in the family.

First-borns, on the other hand, have been found to be achievers who are dominant, conscientious and neurotic. They earn more, are more responsible, anxious and organised, and stick to the rules.

Perhaps one of the reasons they stick to the rules is that parents are normally stricter with their older children. Researchers at the University of Maryland found that parents are more likely to punish their teen's risky behaviour when there are younger children in the family, driven by a desire to set a strict example for these brothers and sisters.

The study found that older children expect stronger penalties because they understand their parents are making an example of them. But as the younger siblings grow up, the parent's resolve tends to dwindle, the researchers say.

"Tender-hearted parents find it harder and harder to engage in tough love' as they have fewer young children in the house and less incentive to uphold reputations as disciplinarians," says Ginger Zhe Jin, one of the authors of the study.

But ultimately, what difference does knowing the results of these studies make to ordinary parents?

"It makes you a little bit more aware of the issues so you can modify or balance your behaviour if you need to," says Siobhan Freegard, founder of the internet parenting forum Netmums.

She points out that with the first child, parents are trying everything out for the first time, so it takes longer.

"These studies might make you more aware that you're treating the eldest child differently, for example," she says.

"But there's a reason for that - you're breaking new ground with your first child."

And she warns: "As a mum you're not expected to be perfect, you're asked to be good enough. Parents shouldn't let these studies make them feel guilty."