If Amazon wants to ensure that customers' responses to an online survey are confidential and the sampling method is unbiased, which approach should be taken?

The approach that involves identifying each randomly selected customer by a random number and using simple random sampling is ideal for ensuring that survey responses remain confidential and that the sampling method is unbiased.

Simple random sampling allows every member of the target population an equal chance of being selected for the survey, which helps eliminate bias that could occur when choosing participants. By assigning a random number to each customer, Amazon can maintain confidentiality, as the identity of the respondents is not directly linked to their responses. This promotes honest feedback, as customers may feel more secure when their answers remain anonymous.

The approach also guarantees that the sample is representative of the broader customer base, thus leading to more valid and generalizable results about customer opinions. This is crucial when the goal is to understand customer satisfaction or collect feedback for improvements.

Other methods, such as surveying all customers in-store or only focusing on frequent customers, could introduce biases and do not ensure that each customer's feedback is confidential or equally represented. Similarly, conducting phone interviews may be less efficient and could compromise confidentiality as well, depending on how the interviews are structured.