Parents can no longer deny what scientists have confirmed - there is always a favorite child.

In his book, Jeffrey Kluger wrote whether we admit it or not, parental favouritism is only natural in human behavior.

"It is my belief that 95 percent of the parents in the world have a favourite child, and the other five percent are lying," he muses in The Sibling Effect: What the Bonds among Brothers and Sisters Reveal about Us.

Kluger's figures may not be a result of a scientific study. But he does cite a research, which is a Californian study of 384 families, who were visited three times a year and videotaped as they go through the regular family dynamics. The study found that 65 per cent of mothers and 70 percent of fathers showed signs of favouritism for one child.

In 2009 two British professors, David Lawson and Ruth Mace, published a study of 14,000 families in the Bristol area. Their study showed that each successive sibling received noticeably less attention from their parents than their predecessors. The study noted older siblings were even fed better, and had higher IQs, presumably an advantage gained from their parents' undivided attention when they were growing up.

Anthropologists refer to Darwinian logic in explaining the Brit study. A firstborn naturally gets overwhelming attention understandably because of parents' excitement over the new experience. Now once you've invested that much in one child, parents tend to continue on that level of attention - a level that may not apply to the succeeding children - if only to protect all the investments made psychologically.

In her feature on Seven Magazine, Jemima Lewis writes this logic has a predictable ending: "favoured children may be left brimming with confidence, or they may suffer from terrible guilt, deliberately sabotaging their own careers or relationships because they don't feel they deserve to be happy. Unfavoured children, meanwhile, may grow up feeling unworthy of love - or they may become adept at finding it outside the family."