Distinguish between an observational study and experiment and know the advantages and disadvantages of each. In your textbooks Math 1342 - Mann, Appendix A, pp. Representative but difficult to do. You randomly sample 20 cold sufferers, administer the pill and check 3 days later.
None have colds.
Control in an experiment you need to compare two groups in which the only likely difference is that one gets the treatment and one does not the group that gets the treatment is called the treatment group and the group that does not get the treatment is called the control group . I am a marketer of athletic shoes and I wish to prove that my shoe makes people jump higher than the shoe made by chief competitor. Placebo effect psychological fact - when people participate in an experiment, even if the treatment itself is ineffective , the participant may experience a change in the observed response variable simply due to his or her expectation of an effect . This is known as the placebo effect. Example - give a group of sick people ordinary sugar pills and many will feel relief .