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Older Siblings Might Be More Influential To A Child Than Parents

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Siblings—it's hard to live with them, but maybe harder to live without them. They're both your first friend and your first enemy. But for those of you with older siblings, research shows that they're more than the people who picked on you as a kid. Older sibs can predict things like your academic success, smoking habit, or even your likelihood to get pregnant. For better or worse, siblings are excellent predictors of adult behavior.

Related: Got Younger Siblings? Your Health May Be Better Off

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They're Watching You!

If you're a younger sibling, you might not want to admit that you watch your big sis or big bro's every move, but it's true. And if you happen to be the older sibling, your parents are right—your younger siblings do notice when you pick up a bad habit, and they're very likely to copy you. 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. Unfortunately, their study focused on smoking.

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The study looked at families where the parents smoked and also those where the older sibling smoked, to measure and compare their influence. As 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. He notes that these findings are magnified in families that are "psychologically and economically unstable." However, Rende feels confident that older sibling's good behavior is "just as contagious as bad."

Siblings can influence bad behavior.... but good behavior too.

Like Sibling, Like Sibling

Siblings don't just give you bad habits, they can also encourage your academic success. This is due to a little something called the "sibling spillover effect" found in a 2014 study. An older sibling can act as a positive role model when they help their younger siblings with homework or give them other academic advice. This is especially true in children with backgrounds where parents may suffer from a language barrier or have less access to information. Investing in the first-born can have a ripple effect for educating their younger siblings.

Related: If Your Mom Calls You Your Sibling's Name, Don't Worry. It Means She Loves You Both

What else? Well, here's a weird one. In a 2009 study by developmental psychologist Patricia East, she discovered that "a woman whose older sister got pregnant was five times more likely to get pregnant than one who didn't." East led this study after realizing that several pregnant teens had visited the OB-GYN clinic she used to work for with their younger sisters at their sides. Within no time, the younger sisters were also pregnant and visiting their office.

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