A paint manufacturer knows that ultraviolet light can degrade many types of paint. It wants to know which paint composition has the least amount of degradation under ultraviolet light. Three different paint compositions were tested. A wall in a windowed hallway of a paint manufacturing plant was divided into 18 sections, and each of the sections was randomly assigned to one of the three paint compositions. The wall sections were painted and then left to be exposed to sunlight. After 18 months of sunlight exposure, the walls were analyzed to determine the degree of change in pigment of the paint, and the results were compared between paint compositions. What are the individuals in this experiment?