"Free range" doesn't necessarily mean the animal is outdoors, or healthier. In the case of free range chickens it only means that they have the potential to leave the 'roost' and go outdoors but a lot of them stay inside, uncaged.

http://www.theglobeandmail.com/life/...rticle1146977/

Ordering free-range chicken at a restaurant may make you feel good, but it turns out you may not be doing the birds any favour.Uncaged chickens are exposed to higher levels of bacteria, parasites and viruses that put them at greater risk for disease and infection compared with their caged counterparts, new research from Sweden's national veterinary institute shows..
Chickens not kept in cages are often housed in shelters where the floor doubles as a giant litter box. As a result, hens have direct contact with bacteria and microorganisms that grow in the litter, which can greatly increase health risks, said the study, available on BioMed Central's journal Acta Veterinaria Scandinavica.
"We found that there was a higher occurrence of bacterial diseases, parasite disease in birds housed in the litter-based systems," said Oddvar Fossum, assistant state veterinarian at Sweden's National Veterinary Institute.
Exacerbating the problem is that hundreds of uncaged chickens are often kept in close quarters, allowing disease and infection to spread quickly.
Housing a large population of uncaged birds in close proximity also leads to increased incidences of pecking, which can result in disease or death.