Design of the Month

Coffee and exercise

The following quotation is taken from the Guardian of 31 July 2007.

Scientists led by Allan Conney at Rutgers University, New Jersey, examined the effect of ultraviolet light on mice bred to be hairless, and so particularly vulnerable to the effects of sunlight.

Four groups of mice were exposed to UV-B radiation, but were given different diets and exercise regimes. One group drank caffeinated water, giving them a caffeine intake equivalent to one to two cups of coffee a day. A second group was fed pure water but allowed to exercise on a running wheel. The third group was given caffeine and access to a running wheel, while the fourth did no exercise and had no caffeine.

The scientists later took samples and checked for signs of UV-induced genetic damage. They also looked for evidence of a natural survival mechanism called apoptosis, in which damaged and potentially cancerous cells are forced to commit suicide before they can form tumours.

The tests showed that caffeine alone led to a 95% increase in programmed cell death and there was a 120% increase from exercise alone. But when combined, exercise and caffeine led to a four-fold increase in cell death, suggesting the body was able to rid itself of pre-cancerous cells much more effectively

Details of the study appear in the US journal Proceedings of the National Academy of Sciences.

  1. What were the experimental units and how many of them were there?
  2. What were the observational units and how many of them were there?
  3. What were the treatments and how many of them were there?
  4. What was the replication?
  5. How do you think the design was randomized?
  6. Was the scale of measurement appropriate?

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