Correct: assess final symptoms - Most important final symptoms are defects and delays. I use the term final, because all other sources of waste could end up causing defects and delays. After discovering the delays, for example, we can assess these effects and then try to find the root causes and correct them.
Advantages - This is like the "Year-end accounting": if we have flaws in our approach, most likely it will translate in these kinds of waste.
Disadvantages - It may be too late. We discover the problems late and apply the corrections even later.
Correct early: assess intermediate symptoms - we should consider and discover all known significant sources of waste, including those with delayed effects such as lack of built-in quality (which creates defects and delays later). We should also take into account the trends of wastes. See more on the previous post.
Advantages - The problems are corrected early. For example. we can improve the quality before inducing significant delays.
Disadvantages - Has a good accuracy, but we cannot evaluate exactly how much possible delays and defects are reduced.
Avoid: use past experience. If we know how to avoid the waste, we can do the right thing the first time.
Advantages - that should produce a maximum effect and best work optimization.
Disadvantages - it is not so clear how much waste has been avoided.
Question: When and how can we apply the three approaches?
A simple answer might be to use them in this sequence:
- Avoid, use past experience
- Correct early. What cannot be solved by experience should be discovered and resolved early
- Correct, assess final symptoms. This should be the last line of defense, but it is also very important and must not be skipped.
A better answer will have some additional comments:
- Make an initial assessment based on existent information and metrics. Apply last two steps (corrections) based on historical information.
- Always use conclusions from late steps to learn and shift to the left the optimization.
We need to evolve from correction to prevention
This approach is consistent with Disciplined Agile Guided Process Improvement logic: succeed early instead of failing fast. My recommendation is to use DA Toolkit or any similar guidance in all three steps. At the same time a good experience in using Lean to avoid waste will be very useful.