Following the "Birth Order" Scenario - Fact of Fiction?!

Decades ago, a group of pediatricians and statisticians, doing what both professional groups do so well, collaborated on a formula for the 'recommended' birth time for children to ensure that adequate time is given for the first child to grow, develop, reaps tons of attention, and be mentally and emotionally best capable to welcome the birth of the following sibling in the family. The recommendation was, as I recall to the best of my own knowledge and relying heavily upon what my husband said at the time (an engineer, go figure!) that there should be three and a half years' time between siblings. Both statistically, logically and emotionally, this is quite an intriguing idea.