FRQ 2 A group of scientists seek to answer the question: Is there a relationship between brain size and
intelligence? A group of 100 volunteers are recruited for study. Each volunteer agrees to have their brain
measured and classified as small, medium, or large. They also take an IQ test which classifies them as
above or below average intelligence. The table shows the classification of the volunteers.
Brain size
Medium
Small
Large
Above average
3
29
20
IQ
Below average
7
29
12
(a) Calculate the marginal distribution of brain size. Summarize your findings in a sentence.
Here is a mosaic plot of the results of the study.
100
90
Below Average 10
80
Above Average 10
70
60
Percent
50
40
30
20
10
0
Large
Small
Medium
Brain Size
(b) Describe what this graph reveals about the association between brain size and IQ for the 100
volunteers in the study. Justify your response.