Designing “controlled” experiments

Fisher found that the data from experiments that had been going on for decades was basically worthless because of poor experimental design.

• Fertilizer had been applied to a field one year and not another, in order to compare the yield of grain produced in the two years. BUT
• It may have rained more or been sunnier during different years.
• The seeds used may have differed between years as well.
• Or fertilizer was applied to one field and not to a nearby field in the same year. BUT
• The fields might have had different soil, water, drainage, and history of previous use.

 Too many factors affecting the results were “uncontrolled.”

Sir Ronald Fisher—The “father of statistics”—was sent to Rothamsted Agricultural Station in the United Kingdom to evaluate the success of various fertilizer treatments. (1919)