You are a Project Manager leading a mega construction project. You have noticed that there have been some deviations beyond your expectations. As a PM, you want to control your project and also find the cause of this deviation. Which technique would you use?
Trend analysis
Pareto Chart i.e. 80/20 rule
Root Cause Analysis using Cause and effect diagrams
Variance analysis

I feel the answer should be Root cause analysis but correct answer is variance analysis please explain why?