@theredeeemer there are several independent sources but also the LDS source that i mentioned in a previous post confirms this in one of their studies. Anyway here is a recent reuters news article that confirms it.
http://uk.reuters.com/article/2012/01/30/uk-mormonchurch-idUKTRE80T1CP20120130
A quote from the article:
The LDS church claims 14 million members worldwide -- optimistically including nearly every person baptized. But census data from some foreign countries targeted by clean-cut young missionaries show that the retention rate for their converts is as low as 25 percent. In the U.S., only about half of Mormons are active members of the church, said Washington State University emeritus sociologist Armand Mauss, a leading researcher on Mormons.
Sociologists estimate there are as few as 5 million active members worldwide.