ASQ CQA – 5. Quality Tools and Techniques Part 12

30. 5E3 Sampling Terms

There is a risk involved in sampling now with this understanding now let’s move on to the next topic here which is sampling terms. In sampling terms, let’s look at this table here we have the actual lot condition, how the lot was and we had that understanding that we have acceptable quality level of 1. 5% or whatever acceptable quality level you have. So the truck or the lot could be good or the lot could be bad the lot will be good. If the items defective in that lot were 1. 5 or less then that was a good lot and the lot would be bad if it had more number of defectives.

But to really find out whether the lot is good or bad you need to check 100% of these items then only you can conclude whether the lot was good or not was bad. But let’s understand that lot could be either good or lot could be bad. Now what we do is we sample that and based on sampling, we made a conclusion we could accept the lot or we could reject the lot. We accepted the lot if in that particular example, if there were three or less number of defectives we rejected the lot if there were four or more number of defectives in that particular sample sample of 80 items.

So here we have accept the lot and reject the lot based on the sampling. Now, we can make mistake here we understand that because of sampling we make a wrong judgment. Now, let’s look at these two green boxes first if the lot was actually good and we accepted the lot, that’s fine. This is what we were expected to do. So nothing wrong with this. So let’s check. Mark this. Similarly, if the lot was bad and we rejected the lot, this is also fine. Because the lot was bad.

That’s the reason we rejected that. So this conclusion is also fine. There is no mistake in that. But then let’s take this particular one which is type one error. If the lot was good and just because of sampling we rejected that lot. This is an error. This error is called as type one error or producers risk. Why producers risk? Because the producer or the supplier who made a good lot and we just rejected that good lot based on the samples which we picked. So the loss will be the producer’s loss because this fellow has sent that truck and now the truck has gone back to the supplier. The supplier’s good lot has been rejected.

The producer’s good lot has been rejected. On the other hand, if the lot was bad and luckily we accepted that based on sampling, then that will be type two error. Type two error is also called as the buyer’s risk because as a buyer the sample came out to be good. Let’s say in those 80 PCs, only two defectives were there in that sample. But actually in the truck there were lots and lots of defectives which we did not pick just because of sampling error. So this is our loss as a buyer because now we have accepted that truck which had lot of defective items.

So these are the two types of errors which you can have in sampling. Type one error, the producer’s risk and type two error, the buyer’s risk. Let’s look at a summary table on the next slide, which will explain this in more details. So here we have a table. On the first column we have type one error. Type one error is also called as alpha. And then on the second column we have type two error, which is also called as the beta. So this is the sign, this is alpha and this is beta. These are Greek letters and we have already said that the type one error is also called as the producer’s risk and type two error is also called as the consumer’s risk or the buyer’s risk. Let’s leave this for a while and come to this one which is example in case of fire alarm. So if you are living in a building and you hear a fire alarm the fire alarm was actually false there. Was no fire, but there was a fire alarm.

If that is the case, this will be called as type one error. So type one error is a false alarm which is leading to inconvenience in case of that truck. Also, this was a false alarm. Everything was good in the truck but we rejected that based on the sampling. On the other hand, in case of fire alarm the type two error will be that when there is actually the fire but the fire alarm did not go so fire alarm did not sound but there was actually fire and because of that the whole building burnt down this is type two error. Type two error could be serious. Sometime when you are accepting critical items, you might accept a bad lot which could be critical for your organization in case of fire alarm also missing fire alarm could lead to disaster. The similar example in case of court will be innocent declared as guilty. The lot was innocent, the lot was good but then we declared this as guilty. We rejected the good lot. So in case of the court term when someone goes to the trial and the person was innocent. But this fellow was declared guilty based on the samples. Based on the evidences, this will be called as type one error. And type two error will be the guilty. Declared as innocent. In most of the countries, the court has a criteria that innocent should not be punished even if a guilty could be released. So they keep focus on this that innocent should not be declared as guilty.

Now what are the effects of that? The effect of the type one error will be unnecessary cost increase because of frequent changes so here we are incurring unnecessary cost and we are making unnecessary adjustment. Whereas in case of type two items we might be producing defects or we might be accepting defects. Type one error is also called as the significance level, significance level or alpha. So if you look here the level of significance or type one error which is also called as alpha, this could be in terms of percentages, you could accept 1% error, you could accept 5% error, you could accept 10% error in case of type one error. So either you can write the type one error or alpha as 1%, 5%, 10%, or you could write in terms of 0. 10. 5 or 0. 0. So this is how you accept or choose an alpha level.

Alpha is the level of significance or the type one error and one minus this will be the confidence level. So confidence level will be zero nine, which is 90% confidence level zero 95 or 95% confidence level or zero 99 or 99% confidence level. So either you select the confidence level or you select the type one error which you can accept. Let’s say I want to accept a 95% confidence level, that whatever things I’m doing, I want to be 95% sure.

In case of type one error, then I will choose confidence level of 95% and that will lead to alpha is equal to 0. 5. These things might look a little bit confusing, but just remember these for CQA exam that when you have type one error, type one error is alpha. Alpha value could be 1%, 5% or 10%. The confidence level will be opposite of that one minus alpha, which is 90%, 95% or 99%. Similarly, one minus the beta is called as the power of the test. Let’s not go too much into those.

31. 5F Change Control

We will look at the change management in context of ISO 9001 requirements and we will look at the configuration management in context of ISO 10,007 requirements. Before we talk about change control, let’s understand that why do we need change? Let’s assume that you are the company who is designing a product and creating that product or producing that product. Now, how changes could happen in this process? Changes could happen because of correction. Let’s say if you did something, if you made something and then there was a problem, then you needed to correct that. This could be in context of something which is a hardware or in case of software as well. So change could happen because of correction, change could happen because of performance improvement. Let’s say over time you have developed this product and you found out ways to improve performance.

And because of that you need to make some changes to your design. And based on that new design, you need to produce the new product. So that’s another way the change could happen in your product. Change could happen for cost reduction, change could happen for safety or reliability improvement. Change could happen for new technology or client needs. Let’s say client needs have changed, client wants something else. Or changes could happen because of regulatory requirement changes and there are few other reasons also because of which the change could happen. Now, the point here in change control is that whatever changes are happening in your design, those changes are translated to your product as well. That’s the purpose of the change control. Now, we said that we will be looking at change control from ISO 9001 perspective. So if you look at ISO 9001 2015, there are two broad areas where the changes are covered. One is changes in the quality management system and the second is changes related to product. Let’s look at these two aspects, starting with changes to the quality management system.

So, here are the requirements of ISO 9001 2015, clause number 6. 3, which is planning for changes. And these are in context of the quality management system changes. So let’s say if you have a quality management system established, you have some rules and procedures established and if you want to make changes to that, what all should happen in that case. So the first requirement here is that when the organization determines the need for change to the quality management system, the changes shall be carried out in a planned manner. And this is very obvious that whenever you are making changes to your quality management systems, your procedures, your work instructions, those need to be done in a planned manner. And when doing this, the organization shall consider the purpose of the changes and their potential consequences. This is also quite obvious that when you want to make changes, you need to understand that why you are making those changes and what are the consequences or impact of those changes. Another very important thing here is the clause B which is integrity of the quality management system.

So when you are making changes you need to make sure that the integrity of the quality management system is maintained because all the processes or work instructions which you are using in the organization are basically interconnected. So if you make a change to one work instruction or the procedure that may affect other work instruction or procedure as well. So you need to take into consideration all these things so that your quality management system integrity is maintained. The next thing when you are making change to the quality management system is to understand the availability of resources and allocation and reallocation of responsibilities and authorities.

If something has changed in the quality management system, instead of let’s say design department, if some particular role now is to be done by the sales department, then those new responsibilities have to be assigned to those persons. So these are the requirements related to the change in the quality management system. Now coming to the second aspect of changes in ISO 9001, which is document changes. And these document changes could be related to, let’s say design change. So if you make a change to the design then how those changes are performed in the organization. So here are the requirement of ISO 9001 2015, version clause number 7. 5. 3, which is control of documented information. The first bullet here is that the documented information required by the quality management system and by this international standard shall be controlled to ensure that it is available and suitable for use when and where it is needed. This is an important clause. So let’s say if you are making changes in the design, so instead of having let’s say dimension of 100 millimeter, the new dimension, you have changed it to let’s say 90 mm. This could be to save cost, this could be to address some safety issue, whatever it is.

But instead of 100 mm now you have changed that product to have a dimension of 90 mm. Now make sure that this particular information which is in the form of drawing is available at the production station, so that people use the right drawing, right instructions. You don’t want that even though you have changed this piece, a particular piece from 100 to 90 mm. But still some of the people are still making those pieces of 100 millimeter dimension which going further in the assembly will not fit and that will cause losses to the organization. So make sure that whatever changes you have made, the right document is available at the right time, at the right place. The second bullet here is that it is adequately protected. So this is not related to change, but your documents need to be adequately protected. But once again this is not related to the change control. So let’s skip that. Come to the second bullet which is for control of documented information. The organization shall address the following activities as applicable. So now let’s come straight away to point number C, which is control of change or the version control. So here what ISO requires is that for control of documented information, and I might have talked earlier as well, that when we say documented information, this means the documents, the work instructions, the procedures or the records. So these should address the change control. That means the documents should have a change control process in place.

Whatever documents you are producing should have, let’s say, a revision number or the date of issue so that you can correctly identify that which of these documents are current and which of these are obsolete. So you need to have a change control or a version control in place. And the general philosophy is, most of the time you will see that each document has a revision number. So if you change the revision number from revision number one to revision number two, then you need to tell all the relevant people that the latest version is revision two. So they should be using revision two, not the revision one, and make sure that this particular information is available at the workplace as well, so that knowingly or unknowingly, someone doesn’t use the revision one when the revision two is the latest version. So these are some of the requirements related to change control in ISO 9001. Now, when we talk of version control, version control could be done in two broad ways. One is a hard copy approach and the second is electronic version control.

So when I started my career, let’s say in 1985, 86, at that time it used to be hard copy control. So what used to happen was, let’s say you created a document, let’s say this is my document, some procedure, and this is Rev. Zero. So if there is some change to this, then Rev. One of this was issued, a hard copy of Rev. One was produced, this was signed by all relevant people and then this is distributed to all the relevant people and how all the relevant people are known. There was a list maintained which tells that to who all this particular Rev. Zero was issued. So all those people who received the control copy of Rev. Zero will get a control copy of Rev one. So this is how a hard copy approach was used for version control. But now with the change of technology, these things are done by electronic version control. So all the documents are produced electronically.

So let’s say now you have, this is my PC. Now, if I open my PC, I see rev. Zero document as the latest version. And then once this is changed to Rev. One, then on my PC I will straight away see Rev one of that document. Something happens in between. All the processes, all the approvals happen in between. And once this document is approved as Rev one, the user will see Rev One. So there is hardly any chance that someone might be still using Rev Zero, because you straighter see rev one on the screen. But the problem with this system is people take a print out of this. So if someone makes a print out of Rev Zero and uses that in Shop Floor, this fellow still might be using REM Zero. So these are something which you need to keep in mind as an auditor. So as an auditor, when you go to Shop Floor, you will pick one of the drawings which people are using, which the workers or the assemblers are using. Then you might want to go and check in the office whether this is the latest revision of the drawing or not.