Are first-borns smarter?

I always told my siblings I was smarter than them. The study mentioned here claims it's possibly true, that there's a 1.5-point decline in IQ with succeeding each child in a family. In honesty though, I told my daughter, who sent the link for this article to me earlier today, that I'm skeptical of the findings. (By the way, she sent the link to me because she found the article "funny." She's the second child.)