The local key body is the main authority that gathers and publishes yearly the industry overview and the local market statistics. That being said, you should expect to find 2011 data on their website or in their publications.
However, before taking this source into consideration, first check their number of members and what percentage of the industry to make, to make sure their facts and figures are relevant and that their representation warrant comes from the majority of the industry players.
Then have a look at their members' list and check for industry leaders: are they present? They should be.
What adds to their credibility, in my eyes, is being part of industry regional / European international organizations or federations. This shows that the association is well-connected and interested in following industry trends, discussing challenges, and importing know-how.
Another sign that the association is legit is their Board of Directors. The board should be composed of elected high-level decision makers coming from the large companies in the industry the association represents.
One more is being cited in the studies done by Big4 consulting companies.
I'll iterate the other two already mentioned in the previous post: the Chairman's voice should be actively heard in the local business and industry publications, and the association should organize industry forums, exhibitions or conferences.
Some very good examples: