McKinsey Problem Solving Test Root-cause Reason Question

1. What is it?

This question gives you a particular set of facts/data and asks you to identify what could be the cause for them. See the picture for an illustration.

1.1 Question format

The following are few examples of typical root-cause reason question format:

  • “Which of the following reasons, if TRUE, will help explain the Facts …”?
  • “Which of the following does NOT explain the Facts …”?
  • “Which of the following points is NOT a valid reason for the Facts …”?

1.2. Root-Cause Reason vs. Fact-Based Conclusion

These questions are often mistaken for Fact-based Conclusion ones, which could slow your study progress in preparation for the test. You can see the differences explained point by point in the table below.

1.3 Example

Facts provided: Visits to the website MConsultingPrep were relatively low last month.

Root-cause Reason Question: What reasons, if TRUE, would help explain the low traffic to MConsultingPrep last month?

The correct answers can be any of the following:

  1. The quality of contents has been bad.
  2. Because of technical issues, some visitors could not access the website.
  3. Last month was December when the overall demand for job prep materials is lowest in the year.
  4. Other new consulting prep blogs opened recently.

Fact-based Conclusion Question: What can be concluded from the data provided?

All of the statements above can be the reason for the stated fact, but NONE of them can be concluded from it.

An example of a statement that can be concluded: Because the conversion rate stayed constant over the years, revenue last month was relatively low.

2. Common pitfalls

What makes a statement NOT a potential reason for a particular fact?

There are two ways a statement cannot be the potential reason: (1) Wrong Subject and (2) Wrong Trend.

  • A statement is (1) Wrong on Subject when the subject is irrelevant, which means the statement have zero effect on the phenomenon mentioned in the stated fact.
  • A statement is (2) Wrong on Trend when the direction is reversed, which usually means the statement has a reversed effect on the phenomenon mentioned in the stated fact

Illustrative example

Let’s continue with the simple example above. The Stated Fact: Visits to the MConsultingPrep blog were relatively low last month.

(1) Example of a “Wrong Subject” statement: “Some new Investment Banking Prep blogs opened recently”

Here the subject “Investment Banking Prep blogs” is irrelevant to the stated fact. The statement (1) will have zero effect on the stated fact.

(2) Example of a “Wrong Trend” statement: “Some other existing Consulting Prep blogs closed recently”

Here, even though the subject “Consulting Prep blogs” is relevant, the trend is reversed. The exit of Consulting Blogs will increase visits to MConsultingPrep. Therefore, statement (2) will have an opposite effect on the stated fact.

3. Challenging Example

You may find the example above too simple to prompt such a complicated approach. We picked a simple example to better convey the concept to you first. However, the same problem on the real McKinsey Problem Solving Test can be much more confusing. Let’s try one right now!

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