从你自己提供的那篇文献看，发展中国家的生育意愿都超过2，从2.5到8.8，那才是正常的。
http://www.associatedcontent.com/article/297295/poll_over_half_of_americans_believe.html?cat=51A majority of Americans, 52%, said that two children is the ideal number to have in a family. One-quarter of Americans (25%), responded that 3 children was the optimal number of offspring within in a clan. A minority, 7% said that 4 children was the ideal number of siblings. With respect to the end ranges, 2% of Americans responded that five or more children was perfect for a family with 3% of survey participants saying that one child was ideal. One percent of Americans thought that having no children was ideal. Nine percent did not know or had no opinion.
The Gallup analysts emphasized that from an average mathematical perspective, Americans believe that 2.5 children is the ideal number of children to have. All in all, an inclusive 56% percent of all respondents thought that small families (2 or less children) was the ideal number of children to have. Conversely, more than one third of Americans (34%) believed that large families (with three or more children) was optimal.