5 Whys

Results are not repeatable - different people using 5 Whys come up with different causes for the same problem.

Causes can be traced back to root causes with the 5 Whys technique.

There are two primary techniques used to perform 5 Whys: the fishbone (or Ishikawa) diagram and a tabular format.

Toyoda developed the concept of 5 Whys: When a problem occurs, ask "why" five times to try to find the source of the problem, then put into place something to prevent the problem from recurring.

Other techniques used in conjunction with PDCA include 5 Whys, which is a form of root cause analysis in which the user asks "why" to a problem and finds an answer five successive times.

The questioning for this example could be taken further to a sixth, seventh, or higher level: the "five" in 5 Whys is not gospel, but five iterations of asking why is generally sufficient to get to a root cause.

The architect of the Toyota Production System, Taiichi Ohno, described the 5 Whys method as "the basis of Toyota's scientific approach . . . by repeating why five times, the nature of the problem as well as its solution becomes clear."