2.9 Optional: Understanding studies

This question is optional; for example, if you need more practice, or you are studying for the exam.

(Answers are available in Sect. A.2)

Fish oil has been touted as helpful to the health of the heart. A newspaper report of one such study (GISSI-Prevenzione Investigators 1999) is shown in Fig. 2.2.

From The Downs Star, Thursday March 18, 1999

FIGURE 2.2: From The Downs Star, Thursday March 18, 1999

Answer these questions:

  1. Identify the variables involved.

  2. Explain whether the study is observational or experimental.

  3. If the study is experimental, determine if the principles of randomization, control, blinding and double-blinding, and blocking have been used. Also determine if it is a true experiment or a quasi-experiment.

    If the study is observational, determine if the study is retrospective, prospective or cross sectional.

  4. Which one of the following, if any, would be a potential lurking variable? Explain.

    • The general health of the subject.
    • The average amount of water consumed each day by the subjects.
    • Gender.
  5. Is a cause-and-effect relationship reasonable? Explain.

  6. What are the limitations of the study?

  7. Identify the units of observation, and the units of analysis.

  8. What did you learn from this report?


GISSI-Prevenzione Investigators. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: Results of the GISSI-Prevenzione trial. The Lancet. 1999;354:447–55.