I downloaded a free ebook by Dr. Kevin Leman last week called What Your Childhood Memories Say About You... And What You Can Do About It: By Dr. Leman. I just wrote a book review about it. He actually has a book called: The Birth Order Book which I have always kept an eye out in second hand book stores and such with no luck. In this free ebook he is offering it does give some insight or childbirth order which you might find helpful, hopefully it is still available for free. The Childbirth Order book unfortunately is not available for free right now but..... it will have more in depth theories. You might find them helpful. The free ebook was available through Amazon. I have a Kindle but you can get a Kindle app for a smartphone even for your computer for free, so do not think you need a Kindle to get the free book. It is exactly the same as the published version. Hope this helps.