Posts Tagged ‘Method’

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Tools to look at Ordered (Ordinal) Data

Monday, November 22nd, 2010

Ordinal data is information that you collect on items that you can rank order some characteristic or attribute.  Examples of this type of data scale is the count of food items on a table that taste excellent, good or bad. Another would the count of dress that are very attractive, look OK, or are ugly. You can see with this type of count data you can arrange the counts in order of best to worse. This scale of data gives us  more information than Nominal scale but not as much as the other types of measurement scales (Interval, Ratio). Scales are ways we collect data.

So once we have done this data collection how can we look at the data to see better what we found? Well for this scale there two types of correlation tools one can use are Pearson correlation, Chi Square which are some what complicated. But one of the simplest is Spearman’s Rank order correlation. In this correlation you are comparing how two people/inspectors/groups  correlate with each other. This will let us know if the two saw things the same way or not.  This could be anything like rating several wine, movies, cars, TV’s etc. For example if you had two friend (x and y) rate 5 movies (A, B, C, D, E) from best(1) to worst(5). you would create the below table and chart to compare your friend results and tell if they look at these movies the same.

Well there you have my thoughts on tools to measure the Ordinal Scale. Next time I am going to discuss the different statistical tool used for the Interval scales of measurement. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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Tools to look at Counts (Nominal) Data

Monday, November 15th, 2010

Just to refresh your mind Nominal Data (Count Data) is information that you collect about the presence or absence of an attribute (characteristic).  Like the number of “naughty” or “nice” kids on Santa’s List. Or, more practical to some, the number of red cars going through an intersection; the number of Order forms with mistakes in them. These counts are all, what we call, nominal scale measurements.  This scale of measurement gives us the least amount of information of the four types of measurement scales (Nominal, Ordinal, Interval, Ratio). Scales are ways we collect data. For instance here we are counting the occurrence of something which is what is called a nominal scale.

So once we have done this counting how can we look at the data to see better what we found. Well for this scale there are a few good tools.

Percentage (%) – This gives you a feel for of all the things you saw, how many were what you were looking for. For example lets say you sat at an intersection and counted red cars going through that intersection in one hour. And during that hour you saw 300 cars go through that intersection and 30 were Red. That would mean that for that hour  10% of the cars that went through it were red. (30 red cars/300 cars through the intersection*100=10%).

Proportion (1/10, 1 in 10) – This, like percentage, gives you a feel for of all the things you saw, how many were what you were looking for. This gives you one other piece of information and that is out of how many you looked at. This, if you are doing the study for yourself, may not be important, but if you are convincing others with a percentage they may want to know how many in the total count. A good example where I like this best is on the internet when looking at customer ratings (those stars showing you that customers really liked the product.  I always want to know how many customers actually rated the product at all. When you see 1 to 5 I am not impressed. But if there was 100 now I feel better about the rating. Remember that 100% liked something out of 1 (1/1) customer is different that 100 (100/100).

Chi-square Test (X2) – There are many times where we want to compare the percentages of items in several different categories. For instance, instead of just red cars we want to collect the number of all cars by color (not just red). It might be, instead of cars, operators, materials, TV channels, Hospitals or any other grouping we might have in mind. In any of these groups your could collect data and place it into different categories (Colors, Sizes, Ratings). The results can be put into what is called a Chi Square Table to answer the question ”Do the groups differ with regard to the proportion of items in the categories?” An example that one could use Chi-square test would be: (The following example is from Narrella(1963) and the Six Sigma Handbook [Pyzdek, 2003]).

Rejects of metal castings were classified by cause of rejection for three different weeks. The question that the Chi-squared test would help answer is: “Does the distribution of rejects differ from week to week?

Well there you have my thoughts on tools to measure the Nominal Scale. Next time I am going to discuss the different statistical tool used for the ordinal scales of measurement. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090




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Measurement

Wednesday, October 20th, 2010

[Note: Most of the information for this article comes from “The Six Sigma Handbook”[i]]

Why do we measure things? To see how things are, or if change has occurred or to understand something. Measurement is just looking at something and describing it in numbers. The rules (mapping functions) that we use to describe the “thing” in numbers provide us with a model of reality. If this model is correct (valid) we can learn about the real world by studying the model and the numbers that it predicts. Without these measurements systems astronomers could not describe the make up of galaxies billions of light-years away from us.

Every questions we have starts in the real world But to understand the question and come up with the answer we use mapping functions (rules) to describe the real world question using numbers. There are times when we map to a non numeric entities in the real world, Like a question about color but we convert these into numbers like the number of red things in a room. These characteristics (elements) are X’s. The “numbers” are Y’s derived using the mapping function as a transfer function of the elements into numbers.

A good example of this we all can relate to is the fuel tank on your car. It would be nice to know how much fuel is in your tank? That would be a measurement of the amount of fuel in your tank.


Real World - Your fuel tank with some amount of fuel in it.

Mapping function – A float with a sensor on a spindle connected to a fuel gage. The gage marked off in numerical intervals. Plus YOU reading the indicator.

Numbers – The gage needle pointing to a numerical value on the gage (like the 1/8 mark just above Empty (0))

Usage – Time to get gas!


Measurement Scales

Not all data (numbers we collect) are created equal. That does not mean some are better than others is just means that some tells us more information than other. You will find that our numbers fall into one of four scales. In teams that I have worked with I always bring up the discussion of measurement scales because not everyone looks at how they would measure something in the same way. Some may look at the fuel tank about as fuel empty or half full, other may talk in gallons of fuel. With that said we need to understand the scale we are going to measure the real world in. The scale of the data to be collected in the measurement process. .So here are the four measurement scales.

  • Nominal Scale – These are numbers that only indicate the presents or absence of an attribute. All we can do here is count items with or without this attribute.
  • Ordinal Scale – This scale gives us a little bit more information. With this scale we can say if an item has more or less of an attribute With this scale we can rank order items.

  • Interval Scale – This scale is use when we are measure the differences between observations. Interval scale numbers that are equally different represent differences of equal magnitude. The zero vale of an interval scale is arbitrary.

  • Ratio Scales – This scale is like Interval Scale except it has a true zero point. In other words you can have nothing less than zero.

Well there you have my thoughts on Measurement and the importance of your scale of measurement. Next time I am going to discuss the different statistical tool use for different scales of measurement. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090



[i] Thomas Pyzdek The Six Sigma Handbook, 2003, McGraw Hill

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Understanding Variation

Tuesday, September 28th, 2010

There is variation everywhere. Look around there are no true clones of anything, everything is at least slightly different. Even in identical twins there is a difference that the parents can see to tell them apart. It is variation in the world that feeds evolution. It is this variation that allows life to survive on this planet. Not everything survives but those that adapt (change/ vary) to the changing world do survive. So as a society we tend to classify things at any given moment. Classification gives us an ability to take a look at things and figure out what makes them “tick” (survive). These classification come in one of two types. Those two types are categorical (discrete) information (data) and numerical (continuous) information (data).

Variation Classifications:

Let’s take a good look at these two types of classification of information I call data. First there is Categorical (discrete) data.

Definitions:

Categorical – Belonging to a category.

Categorize – To describe by labeling or giving a name to a group of characteristics.

Discrete – Apart or detached from others; separate; distinct.

Categorical data can only be one of a limited number of non-numerical choices. It is sometimes, in numerical terms (becomes numerical data), called count data because the only way to measure it is by counting. Examples of this type of data are:

  • Best/better/worse
  • Small/Medium/Large
  • Restaurant $$ ratings
  • Movie ** ratings
  • Pass/Fail
  • Yes/No
  • Red cars
  • Doctors
  • Broken
  • Repaired

Second is Numerical ( continuous) data.

Definitions:

Numerical – of  or pertaining to numbers; of the nature of a number.

Continuous – uninterrupted in time; without cessation.

Numerical data is from a measuring process. Examples of this type of data are:

  • Height
  • Weight
  • Length
  • Depth
  • Voltage
  • Time

Business and Variation:

In businesses we compensate for variation to try to meet customer needs and expectations. This compensation cost money. In Six Sigma we try to understand and deal with this variation. We use statistics to help recognize and thus assess the variation by organizing it in a meaningful way. Statistics help change assumptions to conclusions about where the errors (variations) are and how bad it is affecting our business. Statistics help “Picture” the variation we feel or think is happening.

Definition

Statistic – a numerical fact usually computed from a sample.

Well there you have my thoughts on understanding variation. Next time I am going to discuss measuring that variation and the proper scale of measurement to use depending on the type of  variation you are trying to measure. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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The Element of Time

Friday, September 24th, 2010

As we all know there is variation everywhere and in everything. This includes people pencils, traffic at an intersection, customer needs, goods, services, and of course processes. If you can not predict this variation, I can bet you are compensating for it and that compensation is costing you money!!

In Six Sigma we use statistics to recognize and thus assess and understand that variation so we can predict it ahead of time. This reduces our costs and increases customer satisfaction. Statistics can help you “Picture” variation. Many times we look at data that we gather in various ways but some times we forget about the element of time. At any given point things may look great but over time many times things vary. This variation can not be seen in what we call a histogram of all the data or any other kind of plot that does not use time on one of the axis. For example below (Figure 1) is a plot of Systolic blood pressure of one individual over four months. This plots shows where the average Systolic Blood Pressure would be if it was Normal, Marginally High, or High. In this individuals case it does not look that great.

As you can see this individuals Systolic pressure is all over the place and does not look like a normal distribution. It may be Bi or Multi modal (two or more things effecting the results making several peaks in the Histogram).  From this we can not draw to much of a conclusion but to tell him to see a doctor. Or should we??

If I take that same data and plot over time we get the following graphic.

Now clearly you can see a shift in the blood pressure over the 4 months. All for the better. We might not want the person to see the doctor but find out what might have cause this improvement. A different solution just because we looked at the data in a time sequence chart.

What these two graphs tell us is that if you have collected data over any given time period I’d suggest that you plot it in what is called an x or individuals chart (Figure 2 above) over time and see what you see in patterns there. In fact many times I plot the data in several different ways just to see what I can find. What kinds of patterns I see that can lead me to why the data varies so much.

If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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Elevate the Constraint

Monday, July 12th, 2010

elevate

To elevate a constraint is to make it the number one priority and work on increasing its capacity. Although we have talked bits and pieces of this step in several of the other steps, here we focus on just the constraint. So here are a few ways to elevate the constraint.

  • Add capacity to the constraint. This means adding people and/or equipment. The equipment you add does not have to be new or the same equipment you are currently using, it just has to do the same job even if it runs at a slower rate. This added equipment or personnel  increases capacity.
  • Adjust flow to match constraint. We have mentioned this before and restate it now. What this does is decrease inventory and confusion all over the area. It also makes everyone up and down stream from the constraint aware of the constraints rate (beat of process) and thus the importance of keeping it running.
  • Decouple operations if data verifies this can be done. Some things can be done on products that do not go through the constraint. Other things can be done at the same time (in parallel)  and later coupled up with items going through the constraint.
  • Implement a flexible work cell. A flexible work cell is an work area that can be easily changed or adapted to do several tasks. This goes along with the decoupling. While an operation is waiting on the constraint (one of the seven types of waste),  have it quickly change and do a different task that needs to be done that is not part of the constraints process flow line.
  • Eliminate any non-value added tasks being performed at the constraint. Create a process flow map of the steps that are performed just at the constraint and identify the value added steps and the non value added steps. Totally eliminate the non value added steps or at least remove those tasks from the person working the constraint. Think of the surgeon again, with all the help in the room the surgeon is doing all the value added task while all the help is doing what is considered non value added tasks. These task are now being done in parallel (Decoupled from the flow).
  • Reduce parts handling. Look at the constraint and try to do as much as you can at one holding of an item. Take an item, do what is needed without releasing it and pass it on. If you have to keep turning it over or reloading the item it just adds time and opportunities to create a defect in it.
  • Reduce waiting or storage. Here we want to insure that at the constraint is NEVER waiting for anything. Plus nothing is waiting at the constraint to be used. Now that is near impossible but we want to reduce both of those as much as possible.
  • Reduce or eliminate the process variation. One easy way to do this is by implementing error proofing. Error proofing is a way that when putting two things together there is only one way it can be done. On a form, check boxes are a way of error proofing.
  • Reduce setup at the constraint. Setup is a non value added task and if you can eliminate, reduce or decouple setup you should. Sometimes setup can be done at a step in the process while the step is working. Again look at a surgery room. While the doctor is removing the patients heart, we should be preparing the transplant heart (setup) to be ready for immediate installation. In the pit at the race track, the pit crew does not wait until the car comes in to get the materials that are needed. They have everything laid out ready for the car as soon as it comes in. All this setup is done done while the process (car) is running (still on the track).
  • Reduce Waste – There are seven basic types of wastes that I have talked about in another article. They are: Corrections, Overproduction, Movement of material or information, Motion of employees, Waiting, Inventory, and Processes.  One of the best tools to reducing these wastes is the 5S’s: Sort, Simplify, Sweep, Standardize, and Sustain. Reducing these can save you time and money.

Well there you have how to elevate a constraint in your process. The last of the five steps in constraint management is to go back to step one; Identify the constraint. The reason you start again at step one is that if you have improved the constraint it probably is no longer a constraint and some other step has become the constraint. You continue to do this until the process has no constraints. In other words until the rate of the process exceeds the demand placed on it. You may, in fact, have a slow step but if you still meet demands it is just that; a slow step and not the constraint. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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3rd Step – Subordinate all other Tasks to the Constraint

Thursday, June 24th, 2010

surgeon

In constraint management after you have identified and exploited the constraint, you must subordinate all other tasks to the constraint. If you do not do this all you will have is people wasting time and materials creating parts of a completed product that no one wants. Then you have to spend money keeping track of all the excess inventory until you can use it. It is better to move those resources to helping the constraint task complete its works as quickly as possible. Think of your constraint as the surgeon of the process. All other tasks being performed in the operating room are subordinated to the surgeons work. Materials and tasks are brought in for use right when the surgeon needs them. Here are some helpful hint about subordination.

  1. You can decrease the output of all the rest of the tasks in the constraints process. Tasks before the constraint, will just build up inventory that cost you money. Money tied up in materials and labor to create the inventory that is sitting waiting for processing at the constraint. While it seats you have to keep track of it and store it until you use it. This also happens at tasks after the constraint. Here processes build inventory that sits waiting for the constraints task to be completed before they can complete their task.
  2. Since the capacity of the other tasks is larger than the constraint you can cut back on the utilization of the resources at those task and even move them to help the constraint. Sometimes these resources may not be as efficient as what is at the constraint but every little bit of output at the constraint helps.
  3. Increase the time that the constraint is being run. If the constraint task is only being done Monday through Friday from 8 – 5, then add the weekends or shifts for the constraint, This will increase the overall output of the process.
  4. Make sure that everyone know what the constraint is and what is needed at the constraint to keep it working. Put the information in every tasks written procedures. This way everyone will know the importance of keeping the constraint running and will make it their job to see it is working full time.
  5. Put in place a way to monitor the constraint so everyone know how it is doing at all times. Monitor Constraints throughput and/ or buffer sizes. Information is a great thing when everyone know what is happening and what is important.


Well there you have how to subordinate all the other tasks to the constraint in your processes. Next time I will address how we elevate a constraint. The forth of five steps in constraint management. As always if, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090


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Exploiting the Process Constraint

Thursday, June 3rd, 2010

Exploit ConstraintOnce you have identified your constraints, the next step in constraint management is to exploit them. This mean to utilize them to their maximum extent. To exploit the constraint we have to take a look at a few things first.

  1. We need to look at the existing work in process (WIP) and throughput levels and compare them to the goals or proposed levels or TAKT time for the constraint.
  2. We need to look at the line flow requirements and compare it to the constraint capacity.

These two will give you a feel for how bad things are. Look closely at these comparisons and them do the following things:

  1. Develop a layout depicting buffer locations and sizes. Remember that buffers are one of the Seven Types of Wastes so try to maintain them as low as possible, but never let the constraint run out of raw materials to perform its tasks.
  2. Determine equipment needs. Here we look at if we can find other equipment to help the constraint move product faster. This may include buying more of the same equipment and creating another parallel operation to increase product flow to meet the demand.
  3. Once you have the first two done then adjust the process flow rate to match the capacity of the constraint. This will reduce materials from piling up at the constraint and making thing confusing.
  4. Rebalance operations. Not all products you produce require all operations in the process so something may bypass the constraint or can have other thing performed on it before it needs to go through the constraint. Ignore local efficiencies. Building more products at other operations just to keep people busy does not increase sales it only increases expenses.
  5. Ensure that an operator is always at the constraint working the product through it. Do this by staggering lunches and breaks, and cross training to ensure multiple people can work the constraint. Treat the person working the constraint like a heart surgeon. Everything is always there ready for them to do their job. They don’t have to go looking or wait for anything!!
  6. Establish procedures to ensure the constraint “NEVER RUNS DRY”. This includes material flow management, buffers, inventories, early deliveries, and expediting material so that they are always there at the constraint, ready for use.
  7. Every constraint needs to be a planned maintenance #1 priority so when maintenance is preformed it take the minimum amount of time away from running product on the operation. Notice I said a planned maintenance NOT no maintenance. I do not remember how many times I have heard that “we could not afford to stop for maintenance” but they ended up having to stop for repairs caused by no maintenance. Those repairs took, on average, 10 times longer to do. Maintenance is cheap and can be done off hours on constraint equipment.

Well there you have how to exploit a constraint in your processes. Next week I will address subordination of a constraint the third of five steps in constraint management. As always if, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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Identifying your Process Constraints

Thursday, May 27th, 2010

constraint management

Some times the hardiest thing is to find your process constraint. Remember, a constraint is any resource with less throughput than the demand placed on it. They regulate the output of your whole process. First, you need to understand “demand”. Demand is not what the supervisor wants, although many times it feels like it if the supervisor does not understand constraint management. Demand is the rate at which you need to run the process to meet customer needs or demands. If you are not making it for a customer then it is not a demand you really need to meet.

Where do we look for possible candidates as possible constraints? We go walk the process and look for:

  • Areas where a lot of WIP (Work in Process) or material is waiting for processing. This is one of the Seven Types of Wastes.
  • Areas that work a lot of overtime. This is not just paid overtime but also unpaid. If your company is good, employees many times will work extra hours just to make things happen sooner, this counts as overtime also.

At those operations that you see the above happening review the following:

  • Spaghetti Charts (Physical Process Flow Chart) of these operations. Is there a lot of movement?
  • Line balance at these operations. Is the product balance uneven?
  • Constraint Capacity. Is capacity below the demand?
  • The demand on the operation. Are the demands real?

If the answer to any of these four questions is yes this step is a possible constraint.

To validate these steps as a constraint we need to use TAKT time to understand the constraint need. TAKT time is the time which should be taken to produce a product based on customer demand. With that said if every step or operation of a process is working at or above that rate then the whole process is meeting the customer demand. It only takes one step of the process to be below that TAKT time to make the whole process fail to meet the demand placed upon it. Once we have the TAKT time, we can compare it to the actual throughput and validate the step as a constraint or not. TAKT time is the total net operating time per shift or day, divided by the total customer(s) requirements needed per shift or day. Net operating time is the total time minus breaks and lunch (if things are not running during that time). For example lets say your customer demands are 1000 (parts, transactions, assemblies) per shift and a shift is 8 hours or 480 minutes. Now lets say that we have two 20 minute breaks during the shift and no lunch breaks (employees do take lunch but the operation is still running). That means our net operating time is 440 minutes (480- 20- 20= 440). So TAKT time is 440/1000 = .44 minutes or (.44min * 60 seconds) 26.4 seconds per item. That means that in this process every step has to complete their tasks in 26.4 seconds.

Once you have the TAKT time for each of the process step that you had identified above then you can list all those steps by TAKT time and actual time. Those that exceed the TAKT time are constraints; those that do not exceed the TAKT time are not constraints.

Well there you have how to identify a constraint in your processes. Next week I will address exploiting the constraint the second of five steps in constraint management. As always if, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.


Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090



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A Proper Pareto Chart

Friday, May 14th, 2010

A Pareto Chart is one of the simplest and most powerful tool to guiding you to the root cause of a issue you have.  Many people create Bar charts and call them Pareto, but a proper Pareto shows the 80%/20% Pareto Principle extremely well. That principle being that 80% of the effects come from only 20% of the causes. Below is a video by Thomas Pyzdek showing you how to create a proper Pareto in Microsoft Excel 2007.

If the above is not linked to the video here is the URL:  http://www.youtube.com/watch?v=_1AlJvmW98k

If you have any questions you can comment below or contact me on my website or phone below.

Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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Posted in Six Sigma Tools | No Comments »

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