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Cannabis Campaigners' Guide News Database result:
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UK: Can you produce scientifically meaningful results by studying only a handful of people? Alok Jha The Guardian Thursday 16 Oct 2003 Yes, but it depends on what you're measuring. Scientists in New York announced earlier this week that smoking cannabis regularly could impair male fertility. In a study of 22 cannabis smokers and 59 fertile men, Lani Burkman, a researcher at the Buffalo University school of medicine, found that the sperm from the smokers moved "too fast, too early". She concluded that the active ingredients in cannabis must be doing something to affect the sperm. The story made the newspapers, including this one, but with only 81 people on the trial, can it really be meaningful? Sample sizes are normally huge - epidemiological studies, for example, typically use tens of thousands of people to give statistically sound results. Roy Anderson, a professor of infectious disease epidemiology at Imperial College London, says that if whatever is being studied has big enough effects, a sample size of just 10 people could provide useful results. For example, height distributions by age normally have little variance over large populations. If you wanted to check, say, whether a chemical pollutant is affecting people's height at a certain age (and the effect of the chemical was big enough), you could probably do it with a relatively small sample population. Drug testing require thousands of people however. The exact number depends on what the trials are meant to show. If doctors want to claim that their latest medicine can cure a certain percentage of people with a particular disease, for example, there are specific calculations that will work out how many people should be involved in a trial to prove the claim.
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