Two popular brands of plant fertilizers for home use are Plantx and Earthy. A gardener would like to compare their effectiveness on her collection of new green bean plants. After measuring the height of each of these green bean plants, she randomly assigns each plant into one of two garden boxes, resulting in plants per box. Both garden boxes are kept in similar conditions in regards to such elements as temperature, amount of sunlight, and amount of water. She then randomly chooses one box to be fertilized with Plantx, and she fertilizes the other box with Earthy. She measures all of the plants again when the growing season has finished, and she compares the increases in height between the two groups of plants. Required:
Choose whether the procedure described above is an observational study or a designed experiment. Then further categorize the procedure by choosing the correct type of observational study or designed experiment.