Biologists designed an experiment to test the effect of compost on the development of root crops. They tested several different crops, including carrots, potatoes, beets, and onions. They grew most of the plants in the greenhouse, but due to space issues, they had to grow some outdoors. They gave all the plants the same amount of compost. They obtained the compost from a local farmer and from the local hardware store. They ran out of the farmer’s compost, so some of the plants received that compost when the seeds were planted and other plants got hardware store compost after the plants had already started growing. RESULTS: Some of the roots seemed really big. Other roots seemed normal or small.

CONCLUSION: They couldn’t tell what the effect of the compost was because the results were inconsistent.

What are five problems with this experimental design that could have caused inconsistent results?