## 5.11 **Drills**: Computational exercises

*(Answers are available in Sect. A.5)*

These **Drill** exercises (repeated practice) give you practice at getting computations correct,
and using your calculator.
These drill questions are more about practising the underlying *mathematics* rather than the *statistics*.

**ask**.

A study of drivers in (McEvoy et al. 2006) in New South Wales (NSW) and Western Australia (WA) were asked if they use their phone while driving (Table 5.4).

- What
**percentage**of people use their phone while driving? - What are the
**odds**that a person uses their phone while driving? - What are the
**odds**that a WA resident uses their phone while driving? - What are the
**odds**that a NSW resident uses their phone while driving? - What are is the
**odds ratio**that a person uses their phone while driving, comparing WA residents to NSW residents?

- What

Uses phone | Does not use phone | |
---|---|---|

NSW | 381 | 295 |

WA | 345 | 326 |

- The data in Table 5.5 give the number of plum cuttings that were alive or dead, and whether the rootstock was long or short (Bartlett 1935).
- Compute the
**percentage**of cuttings that were*alive*at the end of the study. - Compute the
**percentage**of cuttings that were*dead*at the end of the study. - Compute the
**percentage**of cuttings that were*long*. - Compute the
**odds**that a cuttings was*alive*at the end of the study. - Compute the
**odds**that a cuttings was*alive*at the end of the study, only for the*long*cuttings. - Compute the
**odds**that a cuttings was*alive*at the end of the study, only for the*short*cuttings. - Compute the
**odds ratio**that a cutting was*alive*at the end of the study, comparing the*short*cuttings to the*long*cuttings.

- Compute the

Alive | Dead | |
---|---|---|

Long | 240 | 240 |

Short | 138 | 342 |

### References

Bartlett MS. Contingency table interactions. Supplement to the Journal of the Royal Statistical Society. JSTOR; 1935;2(2):248–52.

McEvoy SP, Stevenson MR, Woodward M. Phone use and crashes while driving: A representative survey of drivers in two Australian states. Medical Journal of Australia. 2006;185(11–12):630–4.