3. A company wants to survey its employees' attitudes to work. The company's workforce is located at three offices. The number of employees at each location is summarised in the table below.
| Office location | Number of employees |
| Bristol | 856 |
| Dudley | 429 |
| Glasgow | 1215 |
Each employee is located at only one office.
A personnel assistant plans to survey the first 50 employees who arrive for work at the Bristol office on a Monday morning.
- Give two reasons why this survey is likely to lead to a biased response.
A personnel manager has access to the company's information system that holds details of each employee including their place of work.
The manager decides to take a stratified sample of 150 employees.
- Describe how to choose employees for this stratified sample.
- Explain an advantage of using a stratified sample rather than a quota sample.