The first step in the analyze stage is to identify the root causes.
A root cause is the condition or set of conditions that contribute to the creation of problems within a specific process. The elimination or reengineering of the root cause is what will drive improvement, and this is what the objective of Lean Six Sigma is. Just like the roots of a tree, the root cause of a problem may not be visible - data may need to be "shoveled" to unearth it.
There are different ways to identify the root cause(s):
Cause and effect diagram
Data analysis
Process analysis