18 Chapter 1 Basic Ideas iii. What is your marital status? (1) Married (2) Single (3) Divorced (4) Domestically partnered (5) Other a. Are the responses for question (i) nominal or ordinal? b. On question (i), Brenda answers (2) and Jason answers (4). Jason’s answer (4) is greater than Brenda’s answer (2). Does Jason’s answer reflect more of something? c. Jason’s answer to question (i) is twice as large as Brenda’s answer. Does Jason’s answer reflect twice as much of something? Explain. d. Are the responses for question (ii) qualitative or quantitative? e. On question (ii), Brenda answers 2 and Jason answers 1. Does Brenda’s answer reflect more of something? Does Brenda’s answer reflect twice as much of something? Explain. f. Are the responses for question (iii) nominal or ordinal? g. On question (iii), Brenda answers (4) and Jason answers (2). Does Brenda’s answer reflect more of something? Does Brenda’s answer reflect twice as much of something? Explain. Answers to Check Your Understanding Exercises for Section 1.2 1. a. 6 b. Political affiliation, Age, and Voted in last election c. Political affiliation = Democrat, Age = 21, Voted in last election = no 2. a. Quantitative b. Qualitative c. Qualitative d. Quantitative 3. a. Nominal b. Ordinal c. Ordinal 4. a. Discrete b. Continuous c. Discrete d. Continuous SECTION 1.3 Design of Experiments Objectives 1. Distinguish between a randomized experiment and an observational study 2. Understand the advantages of randomized experiments 3. Understand how confounding can affect the results of an observational study 4. Describe various types of observational studies Objective 1 Distinguish between a randomized experiment and an observational study Experiments and Observational Studies Will a new drug help prevent heart attacks? Does one type of seed produce a larger wheat crop than another? Does exercise lower blood pressure? To illustrate how scientists address questions like these, we describe how a study might be conducted to determine which of three types of seed will result in the largest wheat yield. • Prepare three identically sized plots of land, with similar soil types. • Plant each type of seed on a different plot, choosing the plots at random. • Water and fertilize the plots in the same way. • Harvest the wheat, and measure the amount grown on each plot. • If one type of seed produces substantially more (or less) wheat than the others, then scientists will conclude that it is better (or worse) than the others. The following terminology is used for studies like this. DEFINITION The experimental units are the individuals that are studied. These can be people, animals, plants, or things. When the experimental units are people, they are sometimes called subjects. In the wheat study just described, the experimental units are the three plots of land.
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