Fifty patients with brain cancer are divided into two groups. One group receives an experimental drug to fight cancer, the other a placebo. After two years, the spread of the cancer is measured.
While shopping, 425 people are asked to perform a taste test in which they eat two randomly placed comma unmarked candies. They are then asked which candy they prefer.
Fifth-grade students are randomly divided into two groups. One group is taught math using traditional techniques. The other is taught math using a reform method. After 1 year, each group is given an achievement test to compare its proficiency with that of the other group.
For example, a group of old men are divided into two groups; group 1 will breath in smoke and group 2 will not to determine who will get lung cancer. Well they havent accounted for if they were previously smokers.