The key to understanding statistics is finding the sources of information being used to generate those statistics. Whenever a survey is conducted, there is automatically a margin for error that accounts for the families that did not respond to the survey. Those who participated may have all had something in common, such as the region in the U.S. where the survey was distributed, that can skew the statistics. In the case of international adoption, disputes between the government can lead to an absence in information, such as with adoption statistics regarding Guatemala right now.
It's difficult to find thorough and completely trustworthy statistics, but the adoption community has been operating so long on case studies and estimates, that any statistic with a sound standing is better than what's already out there. Starting in 2000, the U.S. Census made a greater effort in collecting adoption-related information. In 2007, the U.S. Department of Health and Human Services compiled national surveys of adoptive families in a comprehensive chartbook titled Adoption USA. The chartbook looks in-depth at the adoption population and lifestyle that can be used to improve the adoption community in the future.
Adoption-related statistics can help put things in perspective for people, be it the averages in adoption fees, trends in abortions since the 1970s or the contentment of children raised by single parents, gays or in open-adoptions. Not everything in adoption is quantifiable, but there is value in what we can put a number and standard to.