Keniese m. Chapter 4 Homework 4.1 Introduction to Experimental Design 1. What is the placebo effect? Placebo is an inactive treatment, for example birth control pills have two pills that are placebo also called " sugar pills" The substance, or placebo , has no known medical effect. It is designed to seem exactly like the real treatment, yet the substance has no actual effect on the condition it purports to treat. 2. (a) Does the following describe an observational study or a designed experiment? Researchers wanted to determine whether there is an association between cell phone use and brain tumors. They followed 555,010 middle aged men over a period of 5 years. During this time there were 113 incidences of brain tumors. The researchers compared the men who never used a cell phone to those who used cell phones and found no significant difference in the rate of brain tumors between the two groups. observational study, studying a scenario in an already existing setting. there is no control group. (b) Does the following describe an observational study or a designed experiment? Researchers wanted to determine whether there is an association between exposure to cell phone radiation and brain tumors in rats. They randomly divided 450 rats into two groups. One group was exposed to cell phone radiation daily and the other group was not. After 5 years there was no significant difference in the rate of brain tumors between the two groups. Designed experiment (c) What are the explanatory and response variables in part (b)? Rats in a controlled setting, exposure to all phone radiation