## A.5 Answers to Lecture 5 tutorial

### A.5.1 Answers to Sect. 5.7

**1.**See Table A.1.

**2.**\(60/320 = 0.1875\). A worker with SMND is 0.1875 times as likely to have worked with metal than not.

**3.**\(33/344 = 0.096\). A worker with SMND is 0.096 times as likely to have worked with metal than not.

**4.**\(0.1875/0.096 = 1.95\); the odds are about twice as great.

**5.**\(60 \div 380 = 15.8\)%.

**6.**\(33\div 377 = 8.8\)%.

**7.**Probably not: big difference seen in a large size sample.

Worked with metals | Did not work with metals | Total | |
---|---|---|---|

SMND cases | 60 | 320 | 380 |

Controls | 33 | 344 | 377 |

Total | 93 | 664 | 757 |

### A.5.2 Answers to Sect. 5.8

**1.**Observational.

**2.**The percentage of residents in each area that detected the smell at the given frequency. So, for example, the first number in the first column would become \(48\div 97\times 100 = 49.5\). This means that \(49.5\)%

*of the sample that lived in Area I*detected the odour at least once a week.

**3.**For example, the percentage of residents who detected an odour at least once a week, who lived in Area I.

**4.**Probably column percentages.

**5.**\(77\div291 = 26.46\%\).