Tools for Problem Analysis

Outline  Cause-and-effect chart  Root cause analysis  Scatter chart

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

Dimension errors Employees Low motivation Poor training Methods Unsuitable process route Unsuitable hardening Environment Wrong coolant Often temperature too low Equipment Poor maintenance Too infrequent tool sharpening

Cause and Effect Chart Fishbone Chart Process Chart

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 is drawn on the right side of the chart and groups of possible causes are identified Cause enumeration: where all possible causes are simply brainstormed and listed in the order they are generated

Fishbone chart with dispersion analysis 1. The chart gives better result when created in group  first step, assemble a suitable group possessing the necessary knowledge 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 large arrow

4. Identify main categories of possible causes  place at branches emanating from 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

5. Brainstorm all possible causes and place these in the 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 the most important ones

Example  Identifying the causes of dimension errors Dimension errors Employees Low motivation Poor training Methods Unsuitable process route Unsuitable hardening Environment Wrong coolant Often temperature too low Equipment Poor maintenance Too infrequent tool sharpening

Process Chart  Variant of Cause and effect chart that directly aimed at improvement of business process  Main steps in the process to be improved are drawn  For each step of the process believed to create problems or contribute to low level performance a fishbone chart is constructed

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

Root cause analysis  Also known as “why-why chart” and “five whys”  The purpose is to find the true root cause of a problem  Can be used in connection with cause- and-effect chart  to ensure if each identified cause really is the root cause of the problem

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 below the 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 the question again and again until no new answer results. This will probably be one of the root causes for the problem  usually requires five rounds of the question “why”  If the question is twisted slightly to asking “how” instead of asking “why” the technique can be used to find root means for reaching a desired state or effect

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

x x xx xxx x x xx Customer waiting time Number of complaints

Scatter chart  Used to show the relationship between two variables  The variables can be process characteristics, performance measures, or other conditions  Usually measured at specified time intervals

Relations in scatter diagram  When one of the factors increases, the other can either also: Increase decrease or display random variation  If the two variables seem to change in synchronization  it might mean that they are related and impact each other Number of defects increases in proportion with the amount of overtime used  Synchronized variation does not always mean that there is a cause-and-effect relationship between variables!

Different Degrees of Correlation Strong positive correlation Strong negative correlation No correlation Possible positive correlation Possible negative correlation

Developing a scatter chart  Select the two variables, one independent and one dependent, to be examined  For each value of the independent variable, the corresponding value of the dependent value is measured Typically, should be at least 30 Preferrably more than 100 data pairs  Draw the chart itself placing the independent variable (the expected cause) on the x axis, and the dependent (effect) on the y axis  Plot the collected data pairs on the chart and analyze it

Interpreting scatter chart  If chart indicates a relationship  variables should be analyzed further to confirm the relationship  Chart showing no relationship should not automatically lead to a conclusion that no relationship exists

Using Scatter chart x x xx xxx x x xx Customer waiting time Number of complaints Diskusikan bersama satu teman: Jika anda adalah seorang pengambil keputusan apa yang akan anda lakukan setelah melihat kedua diagram ini? Number of defects

Aktivitas  Kumpulkan data tinggi dan berat masing- masing anggota kelas  Tentukan dependent variable (Y) dan independent variable (X)  Petakan setiap data dalam sumbu X dan Y  Apa yang dapat anda simpulkan?