To my little boy, there is no-one in this world quite as cool as his big sister.

He wants to play with her and colour with her, and he will watch hour after hour of Barbie, Life in the Dreamhouse and even let her do his toenails the same shade of pink as hers. She is in every way his idol. (Not that I blame him, she is one cool girl, that one!) That is the thing about siblings, though, they are often our closest friends (and, sometimes, worst enemies) and will influence us more than most other people in our lives. In fact, according to a variety of different studies, even more so than our parents will. And for those with older siblings, research shows that they are so much more than the people who pick on you as a kid (which we all know they do!) Apparently, older sibs can predict things like your academic success, smoking habit, or even your likelihood to get pregnant. In fact, for better or worse, siblings are excellent predictors of adult behavior. The reason being younger siblings often pick up on their older siblings' behaviour –and are very likely to copy them. In a 2004 study, Richard Rende, a professor of psychiatry at Brown University, helped find evidence supporting the idea that siblings may be the single most important influence on children. The study, which focused mainly on smoking habits, looked at families where the parents smoked and also those where the older sibling smoked, to measure and compare their influence. Rende told NPR: "Both can have an effect, but in a lot of studies they've found that the effect an older sibling smoking has is greater than the effect that parental smoking has." When one sibling is a smoker, Rende's study found that the other sibling is 25 percent more likely to smoke. The risk is even higher with drinking, at 36 percent. It is also important to note that older sibling's good behaviours are "just as contagious as bad." Phew!