Dr. Nanochick wrote:
I definitely agree that siblings can be heavily influential on each others actions. However, that being said, I don't know how this study can separate the fact that sibling pairs have shared life experiences, and thus, the fact that sibling pairs are more likely to undergo a particular behavior could simply be a result of those shared life experiences, and not necessarily a younger sibling emulating an older sibling...

Yeah this article seems oversimplified. Clearly sisters would share socio-economic circumstances that would increase the probability of teen pregnancy. Furthermore, there are other causal explanations besides behavioral influence:

This study followed 243 younger brothers and younger sisters of parenting teens and nonparenting teens across a 1.5-year period. The average age of siblings was 13.6 years at Time 1 and 15 years at Time 2. Relative to other youths, the sisters of parenting teens exhibited a sharp increase in drug and alcohol use and partying behavior across time and had the highest pregnancy rate at Time 2 (15%). The siblings of parenting teens spent 10 hr a week caring for their sisters' children, and, for girls, many hours of child care was associated with negative outcomes including permissive sexual behavior. Findings suggest that the younger sisters of parenting teens are at very high risk of early pregnancy and that this risk becomes increasingly pronounced across time.

RE: Sibling Influence