Fair enough. Those Wiccans are spreading like wildfire! Either that or they're just starting to "come out of the closet" about their faith... It would be interesting to see how many of those were new recruits vs otherwise. Either way, that's an impressive increase. I wonder what the % is of Muslims...I know its seems hyperbolic but it isn't. its based on 8,000 in 1990 and 342,000 in 2008 I would have liked later numbers but that's the latest i could find. http://www.religioustolerance.org/chr_prac2.htm
Percentage is only a part of calculating growth. Yes, it's important, but without proper context you can't conclude that one group is growing faster than another simply based on one number.the response was based on growth so the percentage is what matters. though based on pure numbers Islam is greater.
*EDIT*
I'd also like to point out some irony in the adverts of the website you chose to link:
