It's not exactly lined out, there leaving out key factors.It is exactly lined out how they did there small pilot study, which might not be totally perfect (but seems to average over 14 flocks), though only the industry has the money to make most studies! As it seems you haven't taken the time to read the article at all, I put the most important findings together:
These amazing results come from 14 flocks around the country that range freely on pasture or are housed in moveable pens that are rotated frequently to maximize access to fresh pasture and protect the birds from predators. We had six eggs from each of the 14 pastured flocks tested by an accredited laboratory in Portland, Ore. The chart at the end of this article shows the average nutrient content of the samples, compared with the official egg nutrient data from the USDA for “conventional” (i.e. from confined hens) eggs. The chart lists the individual results from each flock.
The 2007 results are similar to those from 2005, when we tested eggs from four flocks all managed as truly free range
If you’ve ever been around chickens, you know that whoever wrote that hasn’t. Chickens will spend almost their entire day ranging around a property scratching and searching for food. Even as tiny chicks, they are naturally curious and will begin eating grass and pecking curiously at any insects or even specks on the walls of their brooder box. “Scampering across a field,” looking for food, is precisely their natural way of life.
The main factors are the type of feed/ supplements that was used on test subjects, how long the test took place and type of pasture..
Just a note here.. I'm not disagreeing that home grown eggs can be better than store bought eggs. I am stating there leaving out key factors, and there study could have been nothing more than cherry picking 86 eggs from 14 flocks that were fed a above average feed and or supplements to boost the numbers they were looking for to make there story.