A water purifier company noticed a decline in its closing rate. The person in charge hypothesized that the main cause was the long installation lead time, and in one major region he piloted "installation within 48 hours after reservation" while keeping other conditions as unchanged as possible. Two months later, the closing rate in that region recovered, but during the same period the largest competitor happened to withdraw from the local market. In his report, he said, "The long installation lead time is the main cause, and the verification can be concluded." Which of the following evaluations is the most accurate?

Answer: B

• AThe conclusion holds, because only one factor was changed and the closing rate recovered, so the purpose of small-scale verification has been achieved.✗ Wrong. This corresponds to the misconception that "improvement equals finding the correct cause." A new factor, the competitor's withdrawal, appeared during the period, so the recovery may not be entirely due to shortening the installation lead time. According to step six, the review must continue rather than stop the verification.
• BThe conclusion is drawn too early. The competitor's exit may also have boosted the closing rate. One should check whether other conditions during the same period remained stable and continue observation.✓ Correct. Step six clearly states that the improvement of the problem does not mean the cause has been fully determined, as new factors may intervene. The competitor's exit is exactly such an intervening variable. Only by checking the stability of other conditions and continuing to observe in areas unaffected by the competitor can the cause be attributed.
• CSince there is a confounding factor, the entire verification is invalidated, showing that there is no relationship between installation lead time and closing rate.✗ Wrong. This corresponds to the misconception that "the presence of another cause means the cause in question is ineffective." Important results are often multi-causal. The existence of a confounding factor only indicates that the attribution is temporarily not clean; it cannot be inferred that installation lead time has no relationship with closing rate.
• DImmediately implement same-day installation in all regions, and use a larger-scale improvement margin to finally confirm whether the cause holds.✗ Wrong. This corresponds to the misconception of "replacing review with scaling up." Full-scale implementation has high costs and risks, and different regional conditions make it harder to isolate factors. The correct approach is to continue small-scale testing with controlled conditions.