We are told that a perfume company sends a sample of a new scent to potential customers. Let's consider the sampling method used by the company.
A sample of a new scent is sent to 500 homes. Each person may choose to send back their opinion on the new scent. Each responder has a chance to win a bottle of perfume.
Since a response is voluntary, this is a self-selected sample. We will now determine how this would introduce bias to the results. Let's focus on the highlighted parts of the description of the method.
Reason
Potential Bias
A new scent is sent to only 500 homes.
The sample size is so small that the results may not be valid. Also, since responses are voluntary, the size will be even less than 500.
People choose to send back the opinion.
People who like the scent are more likely to send back their opinion. Therefore, we cannot be sure that the sample is representative of the population of potential customers.
Responders have a chance to win a bottle of perfume.
Customers who did not enjoy either this scent or previous scents would be less likely to send back the opinion because they would not want the free bottle of perfume.
Based on these reasons, the results may be negatively affected and become invalid.
