## 3.2 Using the calculator statistics mode

The data in Table 3.1 give the usage, in tonnes, of polythene by 8 UK cosmetic companies (Gilchrist 2000).

- Using your calculator's
*Statistics Mode*, find the**mean**and**standard deviation**of these numbers. - Without using a calculator, find the
**median**of the data. - Without using a calculator, find the
**IQR**of the data.

8.001 | 29.4 | 266.532 | 4298.7 | 94.5 | 2547.3 | 676.2 | 0 |

Most calculators have **two buttons** that compute the standard deviation: one if the data are a sample, and one if the data are a population.
In practice, data are almost *never* a population.
If you are using your calculator correctly, you should get (before rounding) \(\bar{x} = 990.0791\) and \(s = 1588.514579\).
If you get \(s = 1485.919327\) for the *standard deviation*, you are using your calculator incorrectly, so please **ask for help**.
You are probably pressing the incorrect button to get the standard deviation.

### References

Gilchrist R. Regression models for data with a non-zero probability of a zero response. Communications in Statistics-Theory and Methods. Taylor & Francis; 2000;29(9-10):1987–2003.