To determine whether the results of the survey would be valid, we need to consider a few factors:
1. Sampling method: The survey only includes every third customer who makes a purchase at MacBurger. This method of sampling is called systematic sampling. While it can be a valid sampling technique if the customers are randomly distributed throughout the week, there could still be potential bias. For example, if certain days or times attract different types of customers. It may be more representative to randomly select customers from a range of different days and times.
2. Sample size: The number of customers surveyed is also important. If the sample size is too small, the results may not accurately represent the preferences of all MacBurger customers. A larger sample size generally provides a more reliable representation. The optimum sample size would depend on various factors, such as the total number of customers and the desired level of precision.
3. Response bias: The fact that the survey is voluntary means that not all customers will necessarily participate. This could introduce response bias if the opinions of those who complete the survey differ significantly from those who do not. Additionally, customers may be more likely to answer the survey if they have strong opinions, which could skew the results.
Given these considerations, it is difficult to determine the survey's validity without specific details about MacBurger's customer base, the actual number of customers surveyed, and potential response bias. To improve the validity of the survey, random sampling and a larger sample size could be considered to increase representativeness and reduce bias.