A.2 Answers to Lecture 2 tutorial
A.2.1 Answers to Sect. 2.6
1. Variables: risk of dying from heart disease (or mortality rate? It’s a bit ambiguous) as response; whether they get fish oil and/or Vitamin E as explanatory. 2. True experimental, as fish oil and Vitamin E are given to subjects, and the groups are determined by the researchers. 3. Randomization is not mentioned but probably used (a reporting issue); Control used (there is a placebo). Blinding: Not stated. Blocking: None indicated. Study seems well done, so no obvious lurking variables (however, all subjects did change their diet). Group allocated by researchers, so a true experiment. 4. Since experiment, lurking variables not an issue (if study well done). 5. Cause-and-effect relationship likely (if experiment well done). 6. Limitations: Study only looked at people who have had a heart attack, were on heart medication, and looks like all subjects were Italian, and all subjects changed to a healthy diet. 7. Units of observation: The individuals in the study. Units of analysis: The individuals in the study, as we are comparing the outcomes from each individual, and the outcome from each individual is independent of others.
A.2.2 Answers to Sect. 2.9
1. The first design (A). 2. The third design (C). 3. Depends on the research focus, but the second probably strikes a balance. The key identifying the source of variation that is likely to be the greatest, and allocate relatively more units there because that is the source of variation that is more important to quantify. 4. Easiest would be the design using the smallest number of forests (Design A), as collecting data within a forest is likely to be more convenient than moving around to many forests.