每日一练 | Data Scientist & Business Analyst & Leetcode 面试题 277

Root cause analysis (RCA) is a method of problem-solving used for identifying the root causes of faults or problems. A factor is considered a root cause of removal thereof from the problem-fault-sequence prevents the final undesirable event from recurring; whereas a causal factor is one that affects an event's outcome, but is not a root cause. Though removing a causal factor can benefit an outcome, it does not prevent its recurrence with certainty.

The 5 Whys is a technique used in the Analyze phase of the Six Sigma DMAIC (Define, Measure, Analyze, Improve, Control) methodology. It is a great Six Sigma tool that does not involve data segmentation, hypothesis testing, regression or other advanced statistical tools, and in many cases can be completed without a data collection plan.

The 5 Whys can be used individually or as a part of the fishbone (also known as the cause and effect or Ishikawa) diagram. The fishbone diagram helps you explore all potential or real causes that result in a single defect or failure. Once all inputs are established on the fishbone, you can use the 5 Whys technique to drill down to the root causes.

In the situation where all customers have roughly the same ARPA, and where there is no expansion revenue expected over the lifetime of a customer, you can use this simple formula:

(ARPA is the Average Revenue per Account)

which can also be expressed as follows:

Once again if ARPA is monthly, the churn rate should be monthly.

However in situations where you have widely differing ARPA across the customer base, this would not take into consideration the difference between losing a high value customer versus a low value customer. So a more accurate formula would be:

To truly get an accurate picture of LTV, it is important to also take Gross Margin into consideration. i.e.