[Erik_Mog]

So I was reading through the BJCP 2015 and Brewer's Association 2015 Style Guidelines, and have a question.  Why is there so much difference between the same styles in these?  For example, Marzen:

BJCP 2015
Original Gravity: 1.054-1.060 SG
Color: 8.0-17.0 SRM
Final Gravity: 1.010-1.014 SG
Bitterness: 18.0-24.0 IBUs
Alcohol by Volume: 5.80-6.30 %

Brewer's Association 2015:
Original Gravity (ºPlato) 1.050 - 1.060 (12.4 - 14.7)
Apparent Extract/Final Gravity (ºPlato) 1.012 - 1.020 (3.1 - 5.1)
Alcohol by Weight (Volume) 4.00% - 4.70% (5.10% - 6.00%)
Bitterness (IBU) 18 - 25
Color SRM (EBC) 4 - 15 (8 - 30) 

You can see that there are some pretty significant difference between the two.  For a person that wants to brew to style, how do they choose which guidelines to use?  What is the 'correct' one?

[MDixon]

One is homebrew competitions (BJCP), the other is professional. If you are not going to enter a competition brew whatever suits your fancy.

[mabrungard]

Be aware that the BA Guidelines are broader to make it possible for more beers to be included in a category. That gives brewers greater ability to score a medal and medals are a vital component in commercial beer marketing. However, the BJCP Guidelines are intended to portray what more authentic versions of that beer's category have. The BJCP Guidelines are a sharper picture of each beer while the BA Guidelines are purposely blurred. Hopefully, this helps you decide which to use.

[dmtaylor]

Neither set is more right than the other, and in some spots each is wrong by some ethereal standards.  These truly are just guidelines and may be treated as inputs but never as bibles.

[brewinhard]

As a competitive homebrewer, I tend to stick to the BJCP guidelines more often than not.

[HoosierBrew]

As a competitive homebrewer, I tend to stick to the BJCP guidelines more often than not.

Same here.

[hopfenundmalz]

The BA guidelines are used for the GABF. If you are entering the GABF, then use them. Homebrewers enter BJCP sanctioned competitions, so use BJCP 2015 for those.

[Erik_Mog]

Thanks for the responses.  I was just curious as to why they were different, and now I know.  I have been basing my recipes around the BJCP guide, since that is what is loaded in BeerSmith.  Since I am entering one or two beers in a comp in October, I will stay with the BJCP.