4. Many studies suggest that there is a link between exercise and healthy bones.

Question

4. Many studies suggest that there is a link between exercise and healthy bones. Exercise stresses
bones and causes them to get stronger. One study examined the effect of jumping on the bone
densities of 30 growing rats. There were three jump conditions: a control with no jumping, a
low-jump condition (the jump height was 30 cm) and a high-jump condition (60 cm). After 8
weeks of 10 jumps per day, 5 days a week, the bone density (in mg/cm2) was measured.
(a) Explain why this is an experiment and not an observational study. What are the experimental
units in this study? What is the response variable and the explanatory variable (the factor)?
What are the levels of the factor? What are the treatments?
(b) In designing this study, explain why the rats should be randomized to one of the three different
jump conditions.
(c) Suppose there are 15 male rats and 15 female rats available in the experiment. What is a
block in an experiment? Explain why gender could be used as a block in this experiment.

Explanation / Answer

a)

This is an experimental design. Since the number of factors in order to observe the effect the changes have on one or more response variables.

That is, the number of participants is allocated to the different conditions in an experiment.

The experimental condition is a jump conditions with densities of growing rats in each jump condition.

The response variable is bone densities for different factors and factor is the jumping condition.

The levels of factor is low-jumping factor, high jump factor and control jump factor.

The treatments are the levels of the factor.

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