tools for problem analysis

8/12/2019 Tools for Problem Analysis

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Tools forProblem Analysis


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Outline

Cause-and-effect chart

Root cause analysis Scatter chart


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Cause and effect chart Classical and most widely used tools in quality

management Main purpose is to identify possible causes for an

effect Effect analyzed can be:

An experienced problem Future hoped-for state

Chart can be used for: Finding causes for problem Planning how to reach a state where problem no longer

occur

Types: Fishbone chart Process chart


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Dimension

errors

Employees

Low

motivationPoor

training

Methods

Unsuitable

process

routeUnsuitable

hardening

Environment

Wrong

coolantOften

temperature

too low

Equipment

Poor

maintenance

Too infrequent tool

sharpening


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Cause andEffect Chart

FishboneChart

Process

Chart


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Fishbone Chart

Traditional way of constructing cause-and-

effect charts Main product is a chart that resembles a

fishbone

Two ways of creating the chart:

Dispersion analysis: effect being analyzed isdrawn on the right side of the chart andgroups of possible causes are identified

Cause enumeration: where all possible causesare simply brainstormed and listed in the orderthey are generated


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Fishbone chart with dispersion analysis

1. The chart gives better result when

created in group first step, assemble asuitable group possessing the necessaryknowledge about the area to be analyzed

2. Describe the effect for which causes are

sought e.g. low performance

3. Draw the effect at the end of a largearrow


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4. Identify main categories of possible

causes place at branches emanatingfrom the large arrows

For physical processes

main categories:

People

Machines and equipment

Materials

Methods

Measures

For service processes

main categories:

People

Machines and equipment

Frame conditions

Work environment


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5. Brainstorm all possible causes and place these inthe suitable area of the chart

Brief and succinct description Proceed through the chart one main category at

the time but include surfacing suggestions Causes that belong to more than one category

are placed in all relevant position

6. Analyze the identified causes to determine themost important ones


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Example

Identifying the causes of dimension errors

Dimension

errors

Employees

Low

motivationPoor

training

Methods

Unsuitable

process

routeUnsuitable

hardening

Environment

Wrong

coolantOften

temperature

too low

Equipment

Poor

maintenance

Too infrequent tool

sharpening


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Process Chart

Variant of Cause and effect chart that

directly aimed at improvement of businessprocess

Main steps in the process to be improved

are drawn

For each step of the process believed tocreate problems or contribute to low level

performance a fishbone chart isconstructed


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Low level of work-in-progress

How? Maintain no stock of finished goods

How? Short manufacturing time

How? Run small batch sizes

How? Frequent and swift deliveries from the suppliers

How? Extremely good relationships to the suppliers


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Root cause analysis

Also known as why-why chart and five

whys

The purpose is to find the true root causeof a problem

Can be used in connection with cause-and-effect chart to ensure if each

identified cause really is the root cause ofthe problem


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Root cause analysis procedure Determine the starting point, either a problem or a

high-level cause that should be further analyzed

Use brainstorming to find causes at the level belowthe starting point

For each identified cause, pose the question, why is

this a cause for the original problem?

For each new answer to the question, ask thequestion again and again until no new answer results.This will probably be one of the root causes for theproblem usually requires five rounds of the

question why

If the question is twisted slightly to asking howinstead of asking why the technique can be used tofind root means for reaching a desired state or effect


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Example

Finding means for reducing the amount of work-in-progress in a manufacturing company

Low level of work-in-progress

How? Maintain no stock of finished goods

How? Short manufacturing time

How? Run small batch sizes

How? Frequent and swift deliveries from the suppliers

How? Extremely good relationships to the suppliers


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x

xx x

x xxx

x

x x

Customer waiting timeNumberofcomplaints

h


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Scatter chart

Used to show the relationship between

two variables The variables can be process

characteristics, performance measures, orother conditions

Usually measured at specified timeintervals


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Different Degrees of Correlation

Strong positive correlation

Strong negative correlation

No correlation

Possible positive correlation

Possible negative correlation


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Developing a scatter chart

Select the two variables, one independent andone dependent, to be examined

For each value of the independent variable, thecorresponding value of the dependent value ismeasured

Typically, should be at least 30

Preferrably more than 100 data pairs

Draw the chart itself placing the independentvariable (the expected cause) on the x axis, andthe dependent (effect) on the y axis

Plot the collected data pairs on the chart andanalyze it


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Interpreting scatter chart

If chart indicates a relationship

variables should be analyzed further toconfirm the relationship

Chart showing no relationship should notautomatically lead to a conclusion that norelationship exists


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Using Scatter chart

x

xx x

x xxx

x

x x

Customer waiting timeNumb

erofcomplaints Diskusikan bersama satu

teman:

Jika anda adalah seorang

pengambil keputusan

apa yang akan anda

lakukan setelah melihat keduadiagram ini?

0

2

4

6

8

10

18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

temperature (C)

Number of defects


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tools for problem analysis

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