Part 1: Prepare
Familiarize yourself with the following data.
In 1955, scientists R.R. Sokal and P.E. Hunter analyzed the affects of pesticides on houseflies. Among the data sets they collected were samples of housefly wing lengths. These are normally distributed. The data they collected is summarized in the following frequency distribution.
Normally Distributed | Housefly Wing Lengths |
length (x.1mm) | frequency |
36 | 1 |
37 | 1 |
38 | 2 |
39 | 2 |
40 | 4 |
41 | 6 |
42 | 7 |
43 | 8 |
44 | 9 |
45 | 10 |
46 | 10 |
47 | 9 |
48 | 8 |
49 | 8 |
50 | 6 |
51 | 5 |
52 | 2 |
53 | 2 |
54 | 1 |
55 | 1 |
Source: Sokal, R.R. and F.J. Rohlf, 1968. Biometry, Freeman Publishing Co., p 109. Original data from Sokal, R.R. and P.E. Hunter. 1955. A morphometric analysis of DDT-resistant and non-resistant housefly strains Ann. Entomol. Soc. Amer. 48: 499-507.
Part 2: First Post
Answer these questions:
- Find the mean and standard deviation of the sample of housefly wing lengths. (2 points)
- List the data values that are within 2 standard deviations of the mean. Justify your answer. (2 points)
- What percentage of the data values are within 2 standard deviations of the mean? (2 points)
- Is this consistent with the Empirical Rule? Explain. (2 points)