Inspection deals with error

and rectification. It aims to

from reaching the market.

Quality control uses

to find the root cause of quality problems.

Quality assurance aims to

the organisational responsibility for quality by using quality

The most extensive quality system is

(TQM), which aims to make quality

through team work, staff empowerment, and the involvement of

Statistical process control (SPC) checks a service or product

If there is a problem with the process, it will be

and the problem will be identified and rectified.

Quality of products is tested using

which are plotted on

This process is useful because it requires

There are two categories of statistical tools. Statistical process control assesses whether

assesses the quality of parts or products after they have been produced.

Attribute data are data that

such as the

are data that measure a particular product characteristic such as

Attribute data is also known as

The type of control chart we use for counted data is a

which shows the portion defective in a sample.

Variables data is also known as

The type of control chart we use for measured data is a

The p-chart is a chart used for controlling the

of defective products and services generated.

A

is taken periodically and the proportion of

in the sample is determined.

The control limits are defined as:

= pbar + 3σp

= pbar - 3σp

σp = [pbar(1-pbar)/n]^1/2

n =

pbar =

on the chart, which can either be the historical average defective proportion or a target value

x̄ and R charts are often used together to determine whether a process is in control. The x̄ chart indicates how sample results relate to the

and the R chart reflects the amount of

present in each sample.

To create the x̄ chart, each time a sample is taken from the process, the mean is taken and plotted as a point. The centre line of the control chart is the

i.e., the mean of the sample means. Since the standard deviation is not known, we use the

to calculate control limits as shown:

= x̄bar + A2 Rbar

= x̄bar - A2 Rbar

where x̄bar is the mean of x̄ values, and Rbar is the average range value. The coefficient is equivalent to 3sigma.

In an R chart, the range is the difference between the smallest and largest values in a sample. This range reflects the

instead of the tendency towards a mean value. The formulae for determining the control limits are:

D4 Rbar

LCL =

R bar is the mean of R, where R is the range of each sample and n is the number of samples.

The first level is

someone at this level has had a basic introduction to six sigma, knows why it is used, and how they can contribute.

At the next level, an employee is an

They has had an introduction to how and why six sigma works, 12-16 hours' introduction to statistical reasoning, and an introduction to tools used for simple projects.

A

employee has had an introduction to six sigma processes and tools (typically 40 hours.) They can use these processes and tools to accomplish simple projects, usually in the employees' work area.

At the next level, a

employee acts as a change agent. They have excellent understanding of statistical analysis and tools, which requires as much as 200-240 hours' initial training and lots of continued training. They teach and mentor others, and lead high-level projects.

Finally, a

is a senior level change agent. They have an excellent understanding of statistical analysis and tools, lead highest-level business projects, and teach and mentor black belts.