A disruption of a gene called DYXC1 on chromosome 15 for humans may be related to an increased risk of developing dyslexia. Researchers studied the gene in 109 people diagnosed with dyslexia and in a control group of 195 others who had no learning disorder. The DYXC1 break occurred in 10 of those with dyslexia and in 5 of those in the control group.

(a) Is this an experiment or an observational study? What are the variables?

(b) How many rows and how many columns will the data table have? Assume rows are the cases and columns are the variables. (There might be an extra column for identification purposes; do not count this column in your total.)

(c) Display the results of the study in a two-way table.

(d) To see if there appears to be a substantial difference between the group with dyslexia and the control group, compare the proportion of each group who have the break on the DYXC1 gene.

(e) Does there appear to be an association between this genetic marker and dyslexia for the people in this sample? (We will see in Chapter 4 whether we can generalize this result to the entire population.)

(f) If the association appears to be strong, can we assume that the gene disruption causes dyslexia? Why or why not?