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To choose a lean method, start from the waste, not the toolbox. Changeover time gets SMED, searching gets 5S, slips get poka-yoke, results that differ by shift get standardized work, piles and stock-outs get kanban, long lead time gets value-stream mapping, frequent stops get autonomous maintenance. When a defect or a breakdown has an unknown cause, a root-cause method comes first: 5 Whys for one chain, a fishbone for several suspects, an A3 across departments, DMAIC when there is measured data and months. Answer six plain questions and the tool applies those rules, shows which rule fired, and gives five steps for Monday, what the method will not solve and the free template to open next.

Start withequalsthe method made for the waste (rule R3), or the cause method when the cause is unknown (R4)

Cause methodequalsDMAIC if measured data and months beyond one station; else A3 if it crosses departments; else 5 Whys if fixes did not hold; else fishbone if several suspects or it comes and goes; else 5 Whys

Then, alsoequalsat most two supports: a kaizen event when a team has a week; standardized work to hold the fix (R6)

The whole decision is the ordered rule list in the methodology below. It is an example made for this page from the Lean Lexicon, ASQ, the US EPA lean pages and Smalley's four types of problems, not a standard. Last updated .

One problem at a time. Answer as the floor is today, not as it should be. The result updates as you go and the link carries only your answers, never your name.

What is going wrong

What is going wrong?

Pick the one that costs you most this month. If two apply, run the tool twice and compare.

Your method

Answer question 1 of 6

The method appears after the last question, with why it fits, five steps for Monday and what it will not solve.

The rules are an example made for this page from the sources listed below, not a standard. They point; the people who know the process decide.

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How to use it

One problem, six answers, one Monday

1. Pick one problem. Not "quality"; the thing that cost you most this month, in one line: changeovers on the press, scrap on second shift, the packer that stops twenty times a shift. If you have thirty, answer "many problems" and the tool sends you to a Pareto chart first.

2. Answer as the floor is today. Who is affected, how often, what you have tried, what numbers you have, how much time you can give it. The honest answer to "what have you tried" is the most useful one on the page: a fix that did not hold means the cause was never reached.

3. Read why, not just what. Each method card names the rule that picked it. If the rule does not describe your situation, change the answer and watch the result move. The methodology below prints every rule and its source.

4. Take the five steps to the floor. They are written to start on Monday with the people who do the work, not in a meeting room. "What it will not solve" tells you when to stop and switch.

5. Print or share. The one-page summary prints in black and white on Letter or A4. The link carries your six answers and nothing else, so the team can reopen it and argue with it. Then open the template the card names and begin.

Worked example

Illustrative numbers, not a benchmark

Scrap on a filling line spikes on second shift. The quality engineer has six months of leak-test results by shift and product, three theories from the floor and none proven, and a few hours this week. Answers: scrap, rework or defects; one line or one department; it comes and goes; we looked for the cause: several suspects, none proven; measured data for weeks, by shift, product or machine; a few hours this week, between other work.

  1. 1Is it a gap from standard? Scrap is a defect and the cause is not known, so rule R4 adds a root-cause method before any countermeasure.
  2. 2Which root-cause method? Measured data, yes, but only hours this week, so not a DMAIC project (R4a needs months). One line, not across departments, so not an A3 (R4b). No quick fixes tried, so not R4c. Several suspects: fishbone (R4d).
  3. 3What follows? A fishbone lists candidates and proves nothing, so 5 Whys on the survivor is next (R6d), and standardized work holds the fix on both shifts (R6d).
  4. 4Monday. One hour with both shifts, the technician and the quality engineer: the leak-test failures at the head of the fish, the 6 Ms as bones, then every candidate tested against the six months of data: does it differ between the shifts, products and dates where scrap does and does not spike?
The tool returns: Fishbone diagram (rule R4d), then 5 Whys (rule R6d), then Standardized work (rule R6d). Problem type: gap from standard. Press "Try the worked example" in the tool to see the cards.

Problem to method: the reference table

Last updated

What the rules give for each kind of problem with typical answers: one line or department, every day, nothing tried yet, rough counts, a small team for a week. Your answers move the order; the tool shows how. The table is generated from the same rules as the tool, so the two cannot disagree.

Which lean method to start with for each kind of problem
What is going wrongStart withThenAlsoOpen first
Changeovers or setups take too longSMEDKaizen eventStandardized workSMED changeover worksheet
A machine breaks down or stops oftenAutonomous maintenance5 WhysPareto chartAutonomous maintenance checklist
Scrap, rework or defects5 WhysStandardized work(none)5 Whys template
People make mistakes in the workPoka-yoke5 WhysStandardized workPoka-yoke worksheet
Results differ by shift, operator or dayStandardized workFishbone diagramKaizen eventStandard work sheet template
Time lost searching for tools, parts or information5SKaizen eventStandardized work5S audit checklist
Too much stock, or stock-outsKanbanStandardized workKaizen eventKanban card template
Orders take too long end to endValue-stream mappingKaizen eventKanbanValue stream plan template
A problem that keeps coming back after a fix5 WhysStandardized work(none)5 Whys template
Many problems at once, no agreed priorityPareto chart(none)(none)Pareto chart template

Thirteen methods are covered: 5 Whys, Fishbone diagram, A3 report, DMAIC project, SMED, 5S, Standardized work, Kaizen event, Kanban, Autonomous maintenance, Poka-yoke, Value-stream mapping, Pareto chart. Not covered: 8D, FMEA, statistical process control, hoshin kanri, kata, and any method that is a software product.

The thirteen methods at a glance

What each one is for, who it comes from, and the time the sources describe.

  • 5 Whys

    Ask why the problem happened, then why of each answer, until you reach a cause you can remove. Five is not the point; reaching the cause is.

    Taiichi Ohno, Toyota; the classic example is a machine that stopped because a strainer was missing from a pump. Short for a simple problem; longer when each answer has to be checked at the machine.

  • Fishbone diagram (cause and effect)

    Sort every possible cause of one problem into categories (the 6 Ms) with the people who do the work, then test the candidates against the facts.

    Kaoru Ishikawa; one of the seven basic quality tools. One session with the people who know the job, then the days it takes to test the candidates.

  • A3 problem solving

    The problem, the current condition, the target, the cause analysis, the countermeasures and the plan on one sheet, owned by one person and coached by a manager.

    Toyota; the name is the paper size. Weeks, not hours: the owner works it between reviews with the coach.

  • DMAIC (Six Sigma project)

    Define, measure, analyse, improve, control: a data-driven project for an existing process that misses its standard, led by someone trained in the tools.

    The Six Sigma improvement cycle; the five phases as ASQ describes them. Months, part time, with a trained lead; or a week-long event after the define and measure work is done.

  • SMED (quick changeover)

    Separate the changeover steps that need the machine stopped from those that do not, move the second kind outside the stop, then shorten what is left.

    Shigeo Shingo, 1950s and 1960s; single-minute means under ten minutes. Starts with one timed changeover; the new standard holds only with repeated practice.

  • 5S

    Sort, set in order, shine, standardize, sustain: remove what is not needed, give everything a place, clean to inspect, and keep it that way.

    Japanese workplace practice; the five words are seiri, seiton, seiso, seiketsu, shitsuke. Sort and set in order are the quick part; standardize and sustain are the long part.

  • Standardized work

    The takt time, the one agreed work sequence and the standard in-process stock for a job, written down, posted at the station and trained to every shift.

    Toyota Production System; the baseline that kaizen improves. One job at a time: observe, agree, write, then train every shift.

  • Kaizen event

    A cross-functional team freed from normal duties for one to five days to analyse, change, test and standardize one bounded process, then report.

    The kaizen workshop of the Toyota tradition, as the Lean Lexicon and the US EPA describe it. One to seven days of the team's time, plus preparation and a 30-day and 90-day follow-up.

  • Kanban (pull system)

    A card or signal that authorizes making or moving a set quantity, so nothing is produced or moved without a signal from the process that uses it.

    Toyota Production System; the just-in-time pillar. One loop between two processes first; watch it before adding the next.

  • Autonomous maintenance (TPM)

    Operators clean, inspect, lubricate and tighten their own machines to a standard and tag every abnormality, stopping the deterioration behind minor stops.

    Total productive maintenance, pioneered at Denso in the Toyota group. Starts with one machine's initial clean; the standards and the inspection habit build from there.

  • Poka-yoke (error-proofing)

    A device or design that makes the mistake impossible, or catches it at once: a shape that fits one way, a sensor that stops the line when a part is missing.

    Toyota Production System practice; also called mistake-proofing or baka-yoke. A cheap prototype on one station before any purchase.

  • Value-stream mapping

    A hand-drawn map of every step, wait and information flow for one product family from order to delivery, then a future-state map and a plan to get there.

    Toyota's material and information flow diagram, taught in the West through Rother and Shook's Learning to See. One product family, one leader, one walk door to door; the future state is reached loop by loop.

  • Pareto chart

    A bar chart of problems or causes sorted tallest first, with a cumulative line, so the few that matter most are plain to everyone before any method is chosen.

    One of the seven basic quality tools, as ASQ lists them. Immediate if the counts exist; otherwise the period you decide to count over.

How the decision is made

The frame is Art Smalley's four types of problems (Lean Enterprise Institute, 2018). Type 1, troubleshooting, restores the standard fast: that is the "contain first" note when a customer is affected. Type 2, a gap from standard, needs the cause before the fix: defects, breakdowns, variation, slips and problems that come back get a root-cause method. Type 3, a target condition, raises the standard with the method built for that waste: SMED, 5S, kanban, value-stream mapping, autonomous maintenance, standardized work. Type 4, open-ended innovation, is out of scope. The rules, in the order they are applied:

  1. R1Many problems and no agreed priority: a Pareto chart first, and nothing else until the tallest bar is known.Source: ASQ, Pareto chart: when there are many problems or causes and you want to focus on the most significant.
  2. R2A customer is already affected: contain first (hold and sort stock, protect the customer), then work the cause. The method below is for the permanent fix.Source: Smalley, Four Types of Problems: type 1 troubleshooting restores the known standard quickly before type 2 work finds the cause.
  3. R3Each kind of waste has a method made for it, and that method leads: changeover time gets SMED, searching gets 5S, slips get poka-yoke, variation between shifts gets standardized work, piles and stock-outs get kanban, long lead time gets value-stream mapping, frequent stops and breakdowns get autonomous maintenance.Source: Lean Lexicon entries for each method; Smalley type 3, raising the standard with a method built for that target.
  4. R4aWhen the cause is not known and the problem is a gap from standard (defects, breakdowns, variation, slips, a problem that comes back), a root-cause method is added. With measured data, a project team over months and more than one station at stake: DMAIC.Source: ASQ, DMAIC: for existing processes that miss their standard; long-duration projects of months, led by someone trained in the tools.
  5. R4bOtherwise, when the problem crosses departments or has reached the customer and there is more than a few hours to give it: an A3, so one owner carries the facts and the agreement on one page.Source: Lean Lexicon, A3 Report: the problem, analysis, countermeasures and plan on one sheet, as a management process between an owner and a coach.
  6. R4cOtherwise, when quick fixes did not hold: 5 Whys, because the chain of why stopped at a symptom.Source: Lean Lexicon, Five Whys: keep asking until the root cause is reached and eliminated.
  7. R4dOtherwise, when there are several suspects, or the problem comes and goes, or it is a difference between shifts and operators: a fishbone diagram, to sort the candidates into categories and strike out the ones the facts contradict.Source: ASQ, Fishbone diagram: sorting many possible causes into categories with the people who know the area.
  8. R4eOtherwise: 5 Whys, one chain of cause and effect at the machine.Source: Lean Lexicon, Five Whys, with Ohno's machine example.
  9. R5When the cause is already known, no root-cause method is added. The fix is written as standardized work and, for a slip, built as a poka-yoke; across departments it is carried on an A3.Source: Lean Lexicon, Standardized Work and Error-proofing; Kaizen: no kaizen without a standard.
  10. R6aSupporting methods, at most two: a kaizen event when a team can be freed for three to five days and the lead method changes a bounded area (SMED, 5S, kanban, a value-stream loop).Source: Lean Lexicon, Kaizen (a workshop of about five days); US EPA, Kaizen (one to seven days, a team freed from its duties).
  11. R6bStandardized work follows SMED, 5S and poka-yoke, because the last step of each is to write the new standard and train it.Source: Lean Lexicon, Setup Reduction step six (standardize); Five Ss (standardize, sustain); Standardized Work.
  12. R6cValue-stream mapping follows kanban when the stock problem crosses the plant, and an A3 follows value-stream mapping when the stream crosses departments, to carry the plan.Source: Lean Lexicon, Value-Stream Mapping (door to door, one leader) and A3 Report (used for planning such as value-stream mapping).
  13. R6dA fishbone is followed by 5 Whys on the surviving cause; DMAIC and an A3 are followed by a fishbone inside the analysis; 5 Whys is followed by standardized work to hold the fix.Source: ASQ, Fishbone (candidates, then further analysis); ASQ, DMAIC analyse phase (root cause analysis tools).
  14. R6eWith no numbers at all and a constant problem, a Pareto chart is added so the first week collects counts by category.Source: ASQ, Pareto chart procedure: collect the data, one tally per occurrence with its category.
  15. R6fA one-off breakdown is investigated first (5 Whys), then autonomous maintenance restores the basic conditions so it does not return. Frequent stops get autonomous maintenance first, the investigation second.Source: Lean Lexicon, Five Whys (Ohno's machine example); Lean Lexicon and US EPA, TPM (operators restore and inspect; minor stops as an unrecorded loss).
  16. R6gAutonomous maintenance adds a Pareto of stop reasons when the counts are not yet measured.Source: US EPA, TPM: brief stoppages often go unrecorded.
  17. R6hKanban with one station or line adds standardized work, because the standard in-process stock is one of its three elements.Source: Lean Lexicon, Standardized Work: takt time, work sequence and standard inventory.

Questions are revealed one at a time and the result updates as you answer. No answer is stored and nothing is sent anywhere; the link to a result carries the six answers as short codes and nothing else.

Twelve scenarios, re-derived by hand

The rules were checked against twelve plant problems a lean practitioner would recognize. Each was worked by hand through the rule list and compared with what the tool returns; a unit test runs them on every build. The numbers are illustrative, not customer data.

  • Changeovers on the 400-tonne press take 4 hoursSMED, Kaizen event, Standardized work

    Changeover time is SMED's job (R3); a week with a team makes it an event (R6a); the new sequence is written as the standard (R6b).

    Answers: changeovers or setups take too long; one machine, station or cell; every day, every run; nothing yet; rough counts or a log; a small team for three to five days. Open in the tool

  • Scrap spikes on second shift; several theories, none provenFishbone diagram, 5 Whys, Standardized work

    Defects with an unknown cause are a gap from standard. Several suspects and a shift pattern: fishbone (R4d), then 5 Whys on the survivor (R6d), then the standard that holds the fix (R6d).

    Answers: scrap, rework or defects; one line or one department; it comes and goes; we looked for the cause: several suspects, none proven; measured data for weeks, by shift, product or machine; a few hours this week, between other work. Open in the tool

  • Operators fit the clip backwards a few times a week; everyone knows whyPoka-yoke, Standardized work

    A slip with a known cause: error-proof it (R3), then write and train the standard (R6b). No root-cause method because the cause is known (R5).

    Answers: people make mistakes in the work; one machine, station or cell; it comes and goes; we know the cause; the fix is not in place yet; rough counts or a log; a few hours this week, between other work. Open in the tool

  • The packer on line 3 stops 20 times a shift for a few seconds eachAutonomous maintenance, 5 Whys, Pareto chart

    Frequent minor stops point to deterioration: autonomous maintenance first (R3, R6f), 5 Whys on the top stop reason (R4e), and a tally of stop reasons because they are rarely logged (R6g).

    Answers: a machine breaks down or stops often; one machine, station or cell; every day, every run; nothing yet; rough counts or a log; a small team for three to five days. Open in the tool

  • The main compressor failed last month and nobody knows why5 Whys, Autonomous maintenance, Standardized work

    A one-off failure is investigated as an event (R4e, R6f): 5 Whys at the machine, then restore basic conditions so it does not return (R6f), then the standard (R6d). Plant-wide but only hours to give it, so no A3 (R4b).

    Answers: a machine breaks down or stops often; several departments, or the whole plant; it happened once, or rarely; nothing yet; rough counts or a log; a few hours this week, between other work. Open in the tool

  • Everyone in the tool-room spends time hunting for gauges and fixtures5S, Kaizen event, Standardized work

    Searching is a workplace-order problem: 5S (R3), done as a week-long event (R6a), with the standardize step written as standard work (R6b).

    Answers: time lost searching for tools, parts or information; one line or one department; every day, every run; nothing yet; no numbers, only what people say; a small team for three to five days. Open in the tool

  • Orders take six weeks door to door for three days of workValue-stream mapping, A3 report, Kaizen event

    Lead time is a flow problem across the plant: map the value stream (R3), carry the plan on an A3 because it crosses departments (R6c), deliver each loop with an event (R6a).

    Answers: orders take too long end to end; several departments, or the whole plant; every day, every run; nothing yet; rough counts or a log; a project with a team over two to three months. Open in the tool

  • Assembly runs out of brackets while the warehouse is full of themKanban, Value-stream mapping, Kaizen event

    Stock in the wrong place is a signalling problem: kanban (R3); across the plant the stream is mapped first so the loops land where the waits are (R6c); a week with a team is an event (R6a).

    Answers: too much stock, or stock-outs; several departments, or the whole plant; it comes and goes; we looked for the cause: several suspects, none proven; rough counts or a log; a small team for three to five days. Open in the tool

  • Weld porosity rejects have sat at 4% for a year; lots of data, nobody agrees whyDMAIC project, Fishbone diagram, Standardized work

    A chronic defect with measured data and months for a project: DMAIC (R4a), with a fishbone inside the analyse phase (R6d) and standard work in control (R6d).

    Answers: scrap, rework or defects; one line or one department; every day, every run; we looked for the cause: several suspects, none proven; measured data for weeks, by shift, product or machine; a project with a team over two to three months. Open in the tool

  • The same bearing on the mixer has been replaced three times this year5 Whys, Standardized work

    Replacing the bearing is a fix that did not hold: the chain of why stopped at the bearing (R4c). Once the cause is found, the fix is written as a standard (R6d).

    Answers: a problem that keeps coming back after a fix; one machine, station or cell; it comes and goes; quick fixes that did not hold; rough counts or a log; a few hours this week, between other work. Open in the tool

  • Night shift makes 15% less than day shift on the same line, and each shift blames the other's setupStandardized work, Fishbone diagram

    Two shifts, two ways of working: standardized work is the countermeasure (R3), but first a fishbone with both shifts in the room lists what differs and the measured data strikes out the guesses (R4d). Hours, not a week, so no event (R6a).

    Answers: results differ by shift, operator or day; one line or one department; every day, every run; we looked for the cause: several suspects, none proven; measured data for weeks, by shift, product or machine; a few hours this week, between other work. Open in the tool

  • Thirty open issues on the board and no idea where to startPareto chart

    Too many problems to pick a method for: rank them first (R1) and come back with the tallest bar.

    Answers: many problems at once, no agreed priority. Open in the tool

What this tool does not do

  • It does not know your plant. Six answers cannot carry what the people on the line know; the method card is where the decision starts, not where it ends.
  • It does not diagnose the cause. It picks the method that finds the cause; the finding is still yours, at the machine, with facts.
  • It covers thirteen methods. It does not weigh 8D against A3, size an FMEA, or choose a control chart; the root cause analysis guide goes deeper on the problem-solving tools and the process improvement method selector chooses between improvement frameworks.
  • It does not judge safety. If someone could be hurt, the safety professional's process comes before any method here.
  • It does not replace a coach. Every method on the page works better with someone who has done it before watching the first attempt.

Sources and how this tool was checked

Each source was read in full on 18 October 2026. The method cards quote them at the point of use; here is what each supports.

Unit tests walk all 4,321 combinations of answers to check that each ends in one to three methods with a rule, that the method made for the waste always leads, that DMAIC appears only with measured data and months, that a known cause never gets a root-cause rule, and that the twelve scenarios return what was derived by hand. Books not free to read online, such as Shingo's A Revolution in Manufacturing and Rother and Shook's Learning to See, were not used to check this page.

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FAQ

Lean method navigator: common questions

  1. Start from the waste, not the toolbox. Changeover time gets SMED, searching gets 5S, slips get poka-yoke, results that differ by shift get standardized work, piles and stock-outs get kanban, long lead time gets value-stream mapping, frequent stops get autonomous maintenance. If the problem is a defect or something that keeps coming back and you do not know the cause, find the cause first: 5 Whys for one chain, a fishbone for several suspects, an A3 across departments, DMAIC when you have data and months. If you have thirty problems and no numbers, a Pareto chart comes before any of them.

  2. 5 Whys follows one chain of cause and effect from the problem back to a cause you can remove; Ohno's example runs from a stopped machine to a missing strainer in five steps. A fishbone diagram spreads out instead of down: it lists every possible cause under categories such as materials, machines, methods and people, so a team with several suspects can see them all and strike out the ones the facts contradict. Use the fishbone when there are several candidates or the problem comes and goes, then take the survivor into a 5 Whys.

  3. Both carry a problem from definition to a checked fix. DMAIC is a statistical project: it needs measured data you trust, months of part-time work and someone trained in the tools, and it pays off when the cause is hidden in variation that argument cannot settle. An A3 is a one-page management process: one owner, the facts, the analysis and the plan, reviewed weekly with a coach, and it pays off when the problem crosses departments and the hard part is getting people to agree. A DMAIC project can be summarized on an A3; an A3 does not need a DMAIC.

  4. A format. A kaizen event is a team freed from normal work for one to five days to analyse, change, test and standardize one bounded process. What the team does inside the event is SMED, 5S, a kanban loop, a cell layout or a value-stream loop. The tool adds a kaizen event when you said a team can be freed for three to five days and the lead method changes a bounded area; it does not add one for a problem whose cause needs weeks of data to find.

  5. For most methods, counts are enough: how often, on which shift, which product, which machine, over a few weeks. A downtime log or scrap tickets will do. The one method that needs measured data you trust is DMAIC, and the tool does not suggest it without that. If you have no numbers at all, the tool adds a Pareto chart and tells you to start a check sheet today: every occurrence, with shift, product, machine and time.

  6. No. The rules are an example made for this page from the sources listed in the methodology: the Lean Lexicon, ASQ, the US EPA's lean pages and Art Smalley's four types of problems. They were checked against twelve realistic scenarios by re-deriving each by hand. They point; the people who know the process decide. The free process improvement method selector template on this site is a printable cousin that chooses between improvement frameworks (lean, Six Sigma, PDCA, TQM, 8D); this tool picks the specific lean method for a specific waste.

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