Fraction defective p chart - control charts for attributes, Operation Management

Assignment Help:

Fraction Defective P Chart - Control Charts for Attributes

This type of chart is used when it is impractical or inconvenient to maintain a constant sample size. Instead of plotting the number of defectives in each sample, the proportion (p) or fraction of defectives is calculated and then plotted. Clearly, to ensure that meaningful plots are made, the sample sizes must be large enough to ensure that a number of defectives will typically be found. This may seem to imply that some level of non-conformance is being accepted, but this is not necessarily so. For example, consider the Go/Not-go gauging example shown in the figure on page 249. Whilst the design limits of size on the component diameter might be, say, 24.98 mm and 25.02 mm; for process control purposes the gaps in the gauge might be set at, say, 24.99 and 25.01 respectively. Remembering that, for attributes, only two states are possible (defective/non defective) the relevant probability distribution is the binomial distribution, the mean of which (¯p) can be estimated by inspecting a large number of items:

¯p = total number of defectives/ total number inspected

An estimate of the standard deviation of the binomial distribution (σp), for samples of size n is given by:

σp = √(¯p (1-¯p) / n)

For small values of n the profiles of the binomial distributions are distinctly skewed, but, for large values of n and, particularly, when the product p n is greater than about 5, the distributions are sufficiently symmetrical to be well-approximated by the normal distribution. In this latter situation the control chart limits can be determined in the same manner as for variables charts.

2206_Fraction Defective P Chart - Control Charts for Attributes.png

It will be realised that the implied constant sample size (n) in these expressions presents some difficulty in a procedure when the sample size is allowed to vary. This can be surmounted by using an average value for n, and limiting variation in the size of subsequent samples to, say, ±20 per cent of this value: the results will still be sufficiently accurate for most process control purposes.


Related Discussions:- Fraction defective p chart - control charts for attributes

Explain ethics addressed in the business world today, How are leadership tr...

How are leadership traits and ethics addressed in the business world today?

Describe the global nature of sourcing and distribution, Q1. Discuss The gl...

Q1. Discuss The global nature of sourcing and distribution Q2. Let's also take a look at some examples of organizations and their training programs. Take some time to research a

What are the measures to ensure equal opportunity, Affirmative action refer...

Affirmative action refers to a policy or a program that tries to respond to instances of past discrimination by implementing proactive measures to ensure equal opportunity today. I

Explain a serial entrepreneur who has previously started, You are an invest...

You are an investor in small businesses, and you have three business plans on your desk. Choose one of the potential business owners listed. Explain why you think that would be the

Explain wrongfully discharged have against an employer, Pam worked at a loc...

Pam worked at a local retail store for the past two years. At first, she loved her job; however, the store made a change in management at the end of her first year of employment. T

Why a project manager desires a work breakdown structure, A project manager...

A project manager desires a work breakdown structure that goes through 6 levels of detail. Level 3 through level 6 would most likely be prepared by: Answer Project sponsor

Control charts for variables, Control Charts for Variables  Two comple...

Control Charts for Variables  Two complementary charts are commonly used for the statistical control of process variables. One controls the process mean by monitoring the mean

Explain credit union as opposed to a bank, Jo maintained a checking account...

Jo maintained a checking account at Second Bank. In April, the bank sent her a statement of her account for March, accompanied by the checks that the bank paid. Jo realized that on

Simplex method , Q3. Solve the following Linear Programming Problem using S...

Q3. Solve the following Linear Programming Problem using Simple method. Maximize Z= 3x1 + 2X2 Subject to the constraints: X1+ X2 4 X1+ X2 2 X1, X2 0

Explain crafting a wining business plan, Analyze the steps involved in craf...

Analyze the steps involved in crafting a wining business plan and make at least one recommendation for improving the process. Explain your rationale for making the recommendation y

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd