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Ruxton & Colegrave: Experimental Design for the Life Sciences 2e

Chapter 2

Use these questions to check what you have learned throughout the chapter.

  1. Salmon parr in the wild eat less per day in winter than summer. Suggest hypotheses that could explain this observation. Consider how you could test each of these hypotheses.

  2. Imagine that a study found that people who preferred butter were better drivers than those who preferred margarine. Can you think of any hypotheses that could explain this?

  3. How would you measure driving ability?

  4. Define an indirect measure.

  5. Ecologists commonly use indirect measures such as clutch size, feeding rate, and mass per unit length as indirect measures of fitness. What are the pitfalls of this, and why do ecologists persist in using these indirect measures in the face of these pitfalls?

  6. Can you think of circumstances where ethical considerations might drive you to use indirect measures?

  7. Compare the book’s criterion ‘satisfying the devil’s advocate’ with the legal terms ‘beyond reasonable doubt’ and ‘on the balance of probabilities’.

  8. In the tail-length experiment, we do not want to alter the tail length of individuals assigned to the control group. Why do we bother to cut off their tails then glue them back in exactly the same position?

  9. Discuss how you might test the hypothesis ‘Female humans find blue eyes more attractive than brown’ by both correlational and manipolative means. Discuss the pros and cons of each and which you would choose.

  10. Do you agree with Ronald Fisher’s argument that links between smoking and diseases may not be a direct cause and effect relationship but may be driven by third factors? Justify your view. Why would this link be hard to demonstrate unequivocally?

  11. Explain why we argue that the fact that women who go to university are less likely to marry than those that do not does not imply that going to university does not in itself cause an individual woman to have a reduced likelihood of marriage.

  12. Older drivers are less likely to have accidents. Consider this observation in relation to third variables and reverse causation effects.

  13. Imagine that you are interested in testing the hypothesis that guppies prefer to shoal with individuals that they have encountered previously, compared to strangers. Discuss how you would explore this, both in the field and in the lab. Discuss the pros and cons of each, and which you would choose.

  14. In an effort to convince you of the power of herbal medicine your grandmother says, “I once took ginger when I had a headache and it went quickly”. Why is this not particolarly compelling evidence for the power of herbal medicine? would you be more convinced if instead she said, “I always take ginger when I have a headache, and they always go quickly”?