## 14.9 Exercises

Selected answers are available in Sect. D.14.

**Exercise 14.1 **
A study of hangovers
(Köchling et al. 2019)
recorded,
among other information,
when people vomited after consuming alcohol.
Table 14.11
shows how many people vomited after consuming beer followed by wine,
and how many people vomited after consuming just wine.

- Compute the
*row proportions*. What do these mean? - Compute the
*column percentages*. What do these mean? - Compute the
*overall percentage*of drinkers who vomited. - Compute the
*odds*a wine-only drinker vomited. - Compute the
*odds*that a beer-then-wine drinker vomited. - Compute the
*odds ratio*, comparing the odds of vomiting for wine-only drinkers to beer-then-wine drinkers. - Compute the
*odds ratio*, comparing the odds of vomiting for beer-then-wine drinkers to wine-only drinkers.

Beer then wine | Wine only | |
---|---|---|

Vomited | 6 | 6 |

Didn’t vomit | 62 | 22 |

**Exercise 14.2 **In a study of wallabies at the East Point Reserve (Darwin)
(Stirrat 2008),
the sex of adult and young wallabies was recorded.
In December 1993,
91 males and 188 female *adult* wallabies were recorded.
At the same time,
13 male and 22 female *young* wallabies were recorded.

- For
*adult*wallabies, what*proportion*of adult wallabies were males? - For
*adult*wallabies, what are the*odds*that a female was observed? - For
*young*wallabies, what are the*odds*that a female was observed? - For
*young*wallabies, what*percentage*of wallabies were males? - What is the odds ratio of observing an adult wallaby to a young wallaby, for just the female wallabies?

**Exercise 14.3 **The *Southern Oscillation Index* (SOI)
is a standardised measure of the pressure difference between Tahiti and Darwin,
and has been shown to be related to rainfall in some parts of the world
(Stone et al. 1996),
and especially Queensland
(Stone and Auliciems 1992; Dunn 2001).

As an example (Dunn and Smyth 2018), the rainfall at Emerald (Queensland) was recorded for Augusts between 1889 to 2002 inclusive, for months when the monthly average SOI was positive, and for months when the SOI was non-positive (that is, zero or negative), as shown in Table 25.9.

- Compute the
*percentage*of Augusts with no rainfall. - Compute the
*percentage*of Augusts with no rainfall, in Augusts with a*non-positive SOI*. - Compute the
*percentage*of Augusts with no rainfall, in Augusts with a*positive SOI*. - Compute the
*odds*of no August rainfall. - Compute the
*odds*of no August rainfall, in Augusts with a*non-positive SOI*. - Compute the
*odds*of no August rainfall, in Augusts with a*positive SOI*. - Compute the
*odds ratio*of no August rainfall, comparing Augusts with*non-positive SOI*to Augusts with a*positive SOI*. - Interpret this OR.

Non-positive SOI | Positive SOI | |
---|---|---|

No rainfall recorded | 14 | 7 |

Rainfall recorded | 40 | 53 |

**Exercise 14.4 **A study
(Haselgrove et al. 2008)
asked boys and girls in Western Australia
about back and pain
from carrying school bags
(Table 14.13).

- Compute the
*percentage*of boys reporting back pain from carrying school bags. - Compute the
*percentage*of girls reporting back pain from carrying school bags. - Compute the
*odds*of boys reporting back pain from carrying school bags. - Compute the
*odds*of girls reporting back pain from carrying school bags. - Compute the
*odds*of a child reporting back pain. - Compute the
*odds ratio*of reporting back pain, comparing boys to girls. - Interpret this OR.

Males | Females | |
---|---|---|

No | 330 | 226 |

Yes | 280 | 359 |

### References

*Macropus agilis*). Australian Journal of Zoology. 2008;56:431–9.