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Discussion between Lodge & Musgrave
Arthur S. Lodge     |     home
Needed: statistical analysis
Lodge 1

Can you give me references to justify your claim that moths rest on tree trunks about 25% of the time?

Musgrave 1

Majerus MEN, "Melanism", 1998, Oxford University Press, page 123, Table 6.1 Howlett JJ and Majerus MEN (1987), Biol. J Linn Soc, 30, 31-44.

Lodge 2

In the cited Table 6.1 ("the resting positions of peppered moths found in the wild between 1964 and 1996"), the total number of moths (of all 3 types) is 47, made up of 6 each on exposed and unexposed trunks, 20 on trunk/branch joints, and 15 on branches.

Is a sample size of 47, taken over a period of 32 years, sufficiently large to enable any valid conclusions to be drawn? If it is, what are the confidence limits for such conclusions? In Majerus' book, I could find no discussion of, or mention of the need for, assessments of statistical significance. Presumably such assessments could take into account such factors as the areas and lengths of time of observation, the total moth populations, and the possible failures to observe well-hiddden moths.

Bishop & Cook (Scientific American 232, 1975, p.96) give a population figure of 10 peppered moths per sq. km. per night for one location. In 32 years, there are 11,680 nights. What area and how many nights should be put in to the calculation?

It may be difficult to perform a statistical analysis for this problem, but without it I do not see how we can draw any conclusion about whether the Table 6.1 data are in any way representative of the peppered moth population.