What is the difference between natural and assignable variation in a process?
 

1. a. assignable variation is expected and natural variation can be traced to a specific cause that is not normal to the process
2. b. natural variation is expected and assignable variation can be traced to a specific cause that is not normal to the process
3. c. identifying assignable variation does not require any corrective action to make the process
4. d. both are normal and expected in a process and should not be cause for alarm