A customer service supervisor wants to find out why customers churn, but only surveyed 20 long-standing customers who renewed this year. All expressed satisfaction, and he immediately reported to the boss: "Customer churn has nothing to do with our service." What is the most significant problem with this survey?

Answer: C

• AThe sample size is too small—expanding it tenfold would make the result credible.✗ Incorrect. This reflects a misunderstanding that quantity determines representativeness: even with 200 surveyed customers, if all are renewing customers, the question of why customers churn remains unanswered. The key is covering relevant differences, not the number.
• BPhone interviews are inferior to face-to-face interviews; the collection method affects truthfulness.✗ Incorrect. This misattributes the flaw to the medium: the defect lies not in the interview method but in surveying only renewing customers. Switching to face-to-face interviews would still fail to reveal churn reasons if the same population is surveyed.
• COnly renewing customers were surveyed, missing the most crucial churned customers.✓ Correct. To study why customers churn, churned customers are the most critical group among the target population. By asking only those who stayed, the sample is inherently biased toward satisfied customers, and the conclusion is predetermined by the sample.
• DCustomers who are dissatisfied would not tell the truth anyway, so the survey is meaningless.✗ Incorrect. This is a 'survey futility' fallacy: the possibility that customers may not be fully candid does not invalidate the survey's value. Including churned customers in the sample would yield essential information to answer the question.