In probability case, I usually separate the cost and revenue analysis, and would just do one side of analysis if the case is clearly a cost or a revenue problem.
In a case I did today, the cost of the client's company has gone down, so I focused just on the "revenue side" to analyze. However, in this case, the drop of revenue was actually caused by cost-cutting activity, since the cost-cutting has impacted the quality of the product.
My question is:
(1) Should I always analyze "both" cost and revenue information, in case that I will miss important information? In today's case, I totally did not ask about cost information, which caused me to miss much crucial information.
(2) If the case is clearly a revenue problem (cost did not change, or cost reduced), where should I ask about the cost information? Should I ask during the "finding root cause part", or ask in the cost part after I have fully analyzed the revenue part?