In a classic study examining the relationship between heredity and intelligence, Robert Tryon (1940) used a selective breeding program to develop separate strains of “smart rats” and “dumb rats.” Tryon started with a large sample of laboratory rats and tested each animal on a maze-learning problem. Based on their error scores for the maze, Tryon selected the brightest rats and the dullest rats from the sample. The brightest males were mated with the brightest females. Similarly, the dullest rats were interbred. This process of testing and selective breeding was continued for several generations until Tryon had established a line of maze-bright rats and a separate line of maze-dull rats. The following data represent results similar to those obtained by Tryon. The data consist of maze-learning error scores for the original sample of laboratory rats and the seventh generation of the maze-bright rats.
a. Sketch a polygon showing the of error scores for the sample of original rats. On the same graph, sketch a polygon for the sample of mazebright rats. (Use two different colors or use a dashed line for one group and a solid line for the other.) Based on the appearance of your graph, describe the differences between the two samples.
b. Calculate the mean error score for each sample. Does the mean difference support your description from part a?
c. Calculate the variance and standard deviation for each sample. Based on the measures of variability, is one group more diverse than the other? Is one group more homogeneous than the other?
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