Q 455. Measles Chart or a defect location map was instrumental in improving the survivability of bomber airplanes from enemy fire during World War 2. Explain measles chart and its role in defect reduction along with an example.

 

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 Measles Chart or Defect location check sheet is used for collecting and analyzing data that provides visual image of the item being evaluated.

Usually we collect data of number of defects in a process while working on any process improvement project. But this data has no information on where the defects are occurring in the process. We can use Measles chart for this purpose.

Example: Let's consider example of a plastic chair manufacturing in a company. Instead of just collecting number of defects in the product, we can collect data on location of the defect identified in the product. 

We can draw the picture of the product and mark the location every time where the defect was found. The cluster of marking helps us to identify if root cause of the defect by evaluating up=stream processes.

Measles Chart commonly referred as Defect location check sheet/map is a graphical analysis tool. It can be closely compared to a scatter plot (from clustering viewpoint) in combination to a Defect Concentration diagram. 

 

To use, Measles chart, what we require is the Image of the subject of interest. 
Whenever, there is an issue, we must mark the location of the issue on the Image. 
Depending upon the issue category type, we can use different symbols. Based on the cluster, we shall be able to identify where exactly the issue is frequent and recurring on the Image. This indicates True failures, handling failures and test errors. Thus assisting us in getting into category wise solution mode rite away with a quick turnaround.

 

Below images on the examples can help the operators to quickly identify where defects are happening and could turn their focus to get into root cause of the issue to take actions. Undoubtedly, this helps in defect reduction. 

 

Example 1: Defects in Side by Side refrigerating unit 

 

Example 2: Defects in Adventure touring motorcycle 

 

Example 3: Manufacturing defects in Heavy load transport truck

 

Example 4: Stitching faults in Shirt manufacturing 

 

Example 5: Casual shoe adhesive faults 

 

Benefits of Measles Chart:
Provides visual indication of defects

Easy to deploy 

Effective defect prevention based on the application 
Quantify defects and issues by category and location
Helps to identifying the frequency of the defect occurrence

Can be performed at factory level - production floor. 

 

Precisely, measles charts is a structured analysis that helps in locating, diagnosing and correcting frequent issues / problems on the work floor to improve the operational efficiency. This analysis can help expert teams to retrospect and get into upstream processes to identify and fix the issue enduringly.

 

More reads and a comparative study on Defect concentration diagram, similar subject to that of Defect location map can be seen in the below link:

A measles chart also called defect location chart, is a structured, prepared form for collecting and analyzing data that provides a visual image of the defect (item) to be evaluated rather than just recording how many defects there were.

Normally, we would be able to keep track of the defect rate, and perhaps even use an attribute chart to track, control, and continuously improve the defect rate. What is missing, however, is where the defects are located. 

This is where the defect location check sheet comes in handy. Draw an illustration of the product. Every time a defect is found, the operator or inspector marks the drawing with the location of the defect. 

Let's look at an example, and see how a measles chart can help us visualize defects & their pattern.

Below table shows breakdown data of a fabric dyeing machine of 1 month 

From just one look one will not be able to pinpoint the type of major breakdown and equipment that is resulting in major breakdowns.

Now let us see same data on a measles chart:

 

 

From the drawing now it is much better to visualise the major breakdown type and major equipment where the breakdown is high. 

Hence from the measles chart, one not only visualises the data but also helps the team in identifying the cluster & pattern of the defects and thus result in identifying where one has to focus to reduce defects.

 

 

A Measles chart is also called a defect map or a defect location check sheet. It provides a visual image of the data collected rather than just collecting the count of the number of defects. In addition to the count and rate of defect, it shows the location of the defect.

A drawing of the item is used to plot the place where the defect is occurring. The location of clusters of the defect could throw a better light on the nature of the defects, root cause identification, and its solution.

Measles charts can throw light on the problem either by highlighting the areas where the maximum clusters of the problem occur as in the case of the 1845 Cholera Epidemic or by highlighting the areas where minimum/nil clusters of the problems occur as in the case of the Bomber Aircraft in World War 2.

Examples

Cholera Epidemic.

The cholera epidemic hit Soho, London in 1854.  Dr. John Snow, the father of epidemiology, plotted the location of deaths caused by the epidemic and the location of the pumps. His analysis led to the identification of the source as a contaminated public water pump. The removal of the handle of the pump stopped the epidemic. 

Survivability Bias World War 2

Survivability Bias draws attention to the survivors while evaluating a problem.  Mathematician Albert Wald of the Statistical Research Group, United States did studies on neglected data and came to a conclusion that during World War 2, the retuning combat bombers needed to be strengthened in the areas where the bullet holes were minimum since the places with maximum bullet holes were not causing the aircraft to crash.

A Measles chart of the returning aircraft gave an indication of the areas that showed the strongest part of the aircraft (a cluster of holes) and the most vulnerable parts of the aircraft having areas with no holes. The Measles clusters indicated the parts that were strong and needed the least additional protection.

Defects in Cars

The average number of defects that occur in the body of a car is 67. However, a Measles chart as indicated below show the locations that are more prone to defects.

References.

https://www.sixsigmadaily.com/measles-charts/

https://worldwarwings.com/the-statistics-that-kept-countless-allied-fighter-planes-in-the-sky/

https://www.r-bloggers.com/2013/03/john-snows-cholera-data-in-more-formats/

https://infodreamgroup.com/blog-defect-map-defect-location-advanced-attribute-spc/

Brilliant examples quoted to support the answers. It was a treat to review the answers and select the winner. Winning answer has been provided by Mohamed Asif.