Statistics for laboratory scientists II

Homework problems for lecture 6

1. Consider the following data on the responses of mice to two treatments.

   ttt A:	159	190	204	206	222	223
   ttt B:	370	376	418	488	490	503	512	532	587	605	637

   Assume that these data are independent samples from two normal distributions.

   1. Perform a statistical test of whether the two underlying populations have the same variance. What do you conclude?
   2. Calculate a 95% confidence interval for the ratio of the underlying population SDs.

2. Consider the following (fictitious) data on the weight-gain of lambs on three different diets (from example 11.2 in Samuels and Witmer, pg 468).

   Diet 1	Diet 2	Diet 3
   8	9	15
   16	16	10
   9	21	17
   	11	6
   	18

   A file containing these data is available here: data_hw07-1.csv.

   1. Use R to calculate the ANOVA table and test the hypothesis that the average weight gain for the three diets is the same.
   2. What do you conclude?

3. We consider data on the stem length of daffodils from four sides of a building and from an open area nearby. (Problem 11.12 in Samuels and Witmer, pg 482). Here are some summary statistics:

   Area	Ave	SD	n
   North	41.4	9.3	13
   East	43.8	6.1	13
   South	46.5	6.6	13
   West	43.2	10.4	13
   Open	35.5	4.7	13

   A file containing the data is available here: data_hw07-2.csv.

   1. Plot the data.
   2. Use R to calculate the ANOVA table and test the hypothesis that the average weight gain for the three diets is the same.
   3. What do you conclude?

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Last modified: Mon Apr 11 09:56:34 EDT 2005