The following two graphs show head circumference by sex for 120 female and 64 male biomedical science, medical, nursing, physiotherapy, and radiography students.

In the first figure, a small amount of random variation has been added to the variables so that coincident points can be seen. This is called 'jitter'.

1. What kinds of graph are these?

2. What kind of variable is head circumference?

3. We want to estimate a confidence interval for the difference in head circumference and test the null hypothesis that mean head circumference is equal for male and female students, what methods would we consider?

4. Which of these would be suitable here?

5. The 95% confidence interval, males minus females, = 12 to 25 mm, P < 0.0001. What could we conclude from this?

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Last updated: 27 February, 2009.