4. A New Zealand city council wants to know whether there is sufficient public interest in and support for a proposed new bus service in the city. A survey is undertaken by approaching shoppers as they exit a shopping mall to go to the car park and asking them whether or not they would use this service. The survey is continued until 1000 responses are collected.

Is the resulting sample likely to give biased results? Briefly explain your answer. How could the survey be improved with regard to potential bias?