This thread, in my humble opinion, is the best one on the entire site. I only took one college stats class, so much of this is wayyy over my head, but, the simplicity in how rluzinski describes his points make this a must read. I work in the agricultural odor mitigation field, and often times, we encounter complex systems with many, many variables. One example I am currently working on involves swine finishing barns in my area. Some of this units are experiencing really bad 'foaming' in their manure pits. So bad, that the foam is rising through the slats in the barn floor even. This foam is almost 80% methane, so their is a huge explosion hazard, along with the gas being poisonous to the animals and people that work there. Mass animal kills, human casualties and explosions have happened recently, seemingly with more frequency. Now here comes the crazy part. We have been on swine finishing sites that have multiple buildings housing animals. The buildings were built at the same time, are the same size, and are built with the same materials. Maintenance of each building is the same. There are the same amount of pigs in each building. The pigs eat the same diet, and drink the same water. The pigs in each building are on roughly the same grow schedule. For space reasons, manure had even been transferred between the two pits, so there has been ample mixing of microorganisms, nutrients, etc. That shouldn't even matter though, because the two pits/diff. kind of manures should be the same (and they do test that way in the lab). Despite all that, one building will have severe pit foam, and the other will have no pit foam problems to speak of. I just thought that story was interesting because of the discussion here in this thread. Everything is the same, yet we encounter different results. The beauty of statistical luck. http://forum.brewerfan.net/images/smilies/smile.gif