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10 views

Recaculating control limits when an out of control situation is displayed

When plotting control charts if a point plots outside the control limits then the reason for that point to plot outside is checked and if an assignable cause is found to be the cause then after ...
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24 views

C chart control limits

Can someone please help me to do this problem: A C Chart for non-conforming units is set up with lower control limit $0$ and a center line at $\bar c$. The upper control limit (UCL) for this ...
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20 views

Changing a target value that minimize the product being outside the specifications in quality control

I was doing problems in the article here. In the question on page 16 I don't understand part b) how to find a target value that minimize the product being outside the specifications. Can someone ...
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0answers
48 views

How to name the concept of the mean shift divided by the standard deviation

In the context of a paper dealing with Statistical Quality Control, I am defining and using the concept of the mean shift divided by the standard deviation of a (normally distributed one-dimensional) ...
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0answers
10 views

How to determine if a U chart or a C chart to be used

This is regarding theory of attribute type control charts.In a question it is given data for the number of non confirmities per 1000 meters of wire. I have to calculate control limits for a ...
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0answers
18 views

Calculating $\bar c $ in C chart

In studying C chart I came accross this problem in Statistical Process control by Douglas .C.Montgomary. In this exercise it says: A control chart is used to control the fraction of non ...
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0answers
16 views

Area of Opportunity in C chart and U chart

In the article whether to use C chart of U chart is determined by area of opportunity.But I don't understand what is meant by area of opportunity and how it relates to C chart and U chart.Can ...
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0answers
21 views

Finding n and c in single sampling plan

I am learning a quality control course and in Single sampling scheme for attribute type inspection I don't understand the method used for calculating the values of $n$ and $c$. The method is as ...
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0answers
39 views

Calculation of Average run length in non-normal distribution

I want to calculate Average Run Length(ARL) in non-normal distribution. In a normal distribution, I can calculate the ARL for example, ...
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0answers
13 views

Monitoring high quality near zero defect processes

What are the latest techniques for monitoring discreet defects in high quality processes with defective rates in the parts per million range?
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1answer
44 views

Control limits in $\bar{x}$ and R chart

I am learning a Quality Control course and in theory part I don't understand calculating the control limits for $\bar{x}$ and R chart.I want to know, say when I calculate the R chart control limits no ...
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0answers
12 views

How to get the improvement index in monthly basis for employees absence

I have the following information for each month of the year: Total Absence Days in a given month Total Headcount in a given month I want to get an index in which I can compare months and see if ...
2
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0answers
61 views

Detecting a trend to increase, in a time series, in real time

Probably, someone who's into technical analysis of share prices eats stuff like this for breakfast. Me, I couldn't devise a theoretically acceptable approach. I have this thing (private working set, ...
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1answer
30 views

Use daily production as a check on whether monthly production goal is likely to be met

This is a real small business problem, not a homework problem. A monthly production goal is 60000. We want to be sure that say 95% of months meet this goal. The goal is a minimum, so we want to be ...
2
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1answer
79 views

Quality Control Chart for non-normal distributed data

I am interested in building quality control charts for time series data where every data point has different gradation within the range of 0 to 1. For example first data point X1 may be 0.1, 0.2,..,1 ...
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2answers
932 views

What is “the” correct way of calculating Cp/Cpk values for Statistical Process Control?

There seems to be many different methods of calculating Cp/Cpk values in SPC, and I need help in determining which one to use at any given situation. Currently, we need to show Cp/Cpk values when ...
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1answer
39 views

multivariate control chart

I am trying to build a multivariate control chart but I did not find any good explanation of how to do that. Starting with $x_0$ a part of the samples that are in control I compute $\mu_0$ and ...
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0answers
50 views

Mean number of samples before out of control in p-chart

I'm stuck with this problem on quality control and p-charts. There is a given process, monitored periodically taking samples of 100 items each and counting the number that are defective. In the last ...
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1answer
52 views

Average run length

Suppose in an Xbar chart, k successive points plotted outside a control limit indicates an out of control situation. If p is the probability of plotting a point outside a control limit, how is ARL = ...
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2answers
598 views

Why isn't bayesian statistics more popular for statistical process control?

My understanding of the bayesian vs frequentist debate is that frequentist statistics: is (or claims to be) objective or at least unbiased so different researchers, using different assumptions can ...
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1answer
124 views

On properly setting up a control chart

Let me present to you the way I have being 'doing' control charts up until now. I have a series of $k$ samples of size $n$. I calculate the the sample means $\bar{x}_i$ and the grand mean ...
2
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1answer
214 views

Control charts of seasonal data

I have been asked to develop control charts for my company - or some other means of quickly identifying when ticket sales are "out of control" and not just a random blip. The data we are looking at ...
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1answer
39 views

Control lines that converge?

I'd like to have some control lines that converge, if the random variable observed becomes stable. For example, as the chart below, the variable starts at around 3.0, the upper control line is around ...
2
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2answers
117 views

Meta analysis: How to assess the quality of each of the individual studies in a systematic way?

I have a meta analysis at hand. I have reported on the quality of the included studies in a narrative form. But after I was requested about "quality assessment". I guess it might be something else, a ...
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0answers
91 views

Sampling for quality control

I would like to do some quality control study for a set of manufactured components. For a given set, I can draw several samples. Each drawn sample can be either good or bad. My plan is to create a ...
2
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2answers
69 views

Method to remove bad values in time series (bad values known to take on a particular value)

This sounds easy, but I don't know of a good statistical method for it. I have a time series that has (good) data points that range from ~3.5 to 30. The data are collected by an automated sensor. ...
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0answers
44 views

Non-Analytic extrapolation

I have some samples of a stable real-world process. Its is polymodal, and does not cleanly fit any of the "textbook" analytic distributions. I need to make very accurate estimates of the maximum ...
2
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1answer
279 views

Bootstrap USL/LSL for non-normal data

This is new statistics space for me, so please excuse my ignorance. I have some data (N=180) that isn't normally distributed (verified in Minitab, P<0.005) and I want to use the data to get a +/- ...
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1answer
2k views

Measuring k-means clustering quality on training and test sets

I'm working on implementing streaming k-means in Mahout. The code is mostly done and we're talking about how to integrate the code. As part of the quality evaluations, I want to know how the ...
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0answers
301 views

Control chart Xbar and R missing values

I am taking a business statistics course and I can't seem to figure out how to find the missing figures in the following problem; here's the question: Using the data below, determine the trial ...
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2answers
171 views

Data analysis on multiuser environment

I have following environment that I'd like to analyze. My company is divided in two teams: Insert Team (composed by 150 persons) Quality Check Team (composed by 10 persons) Suppose that all ...
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0answers
35 views

Software quality control references

I'm looking for references on statistical quality control of software. My searches have turned up a lot of writing on how to predict the time that software projects will take, and also software ...
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1answer
110 views

Are $\sigma_{70\%} = cte * \sigma /\sqrt{N}$, & $\sigma_{\bar x_{70\%}} = cte * \sigma /\sqrt{N}$ valid with non-normal distributions?

My working population is non normally distributed and from time to time I need to take a sample of it. Sometimes my sample exists of 100 units, at other times of 150 units. Of my sample I calculate ...
4
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2answers
133 views

Algorithim to determine if point is “too far from the average”

Long story short I have a collection of about 30 scripts that manipulate data sets and place them in a database. These scripts report their running times as well as any errors that occur to a ...
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2answers
677 views

Validating data set using standard deviation

Suppose I have two data sets. The average of one data set is 5.5 secs and the standard deviation is 0.0435. The average of the other data set is 5.2 secs but the standard deviation is 0.5123. I know ...
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2answers
331 views

Where can I find online notes about statistical process control?

Please could you someone help me to find online resources related to the topic of quality control (statistical process control)
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2answers
318 views

How to judge if a datapoint deviates substantially from the norm

This is Statistics 101, but I'm not a statistician and so can't seem to find the right technical jargon to google. My company collects data at discrete points through time. Today's datapoint is ...
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2answers
2k views

How to calculate margin of error for a binomial quality control experiment where only successes are observed (including FPC)?

Wikipedia's Margin of Error entry says that a random sample of size 400 will give a margin of error, at a 95% confidence level, of 0.98/20 or 0.049 - just under 5% given an infinite ...
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2answers
135 views

Looking for aberrations in time based data

Looking at IO latency data for a storage array. When a drive is about to fail, one indication is an increase in the IO operations 'time to complete'. The array kindly provides this data in this ...
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1answer
302 views

How to properly set up hypothesis testing in an operations reporting environment

I am in charge of quality control of n = 400 reports. Most of the quality checks are automated, but some have to be manual. I need to figure out how many reports my team needs to check manually in ...
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1answer
251 views

Color standards for control charts

Are there any references or standards that dictate the color coding of the zones of a Shewhart style control chart. We use green in +/- 2 sigma range, yellow between 2 and 3 sigma and red beyond 3 ...
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134 views

Control Chart Structure - X axis

I am using a computer system with Shewhart control charts. Is it appropriate to use time stamped data as the x axis in a sequential manner. Using this process will create gaps in the control chart, ...
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0answers
108 views

Using control charts for data with non-constant mean?

My company would like to use control charts (Shewhart, EWMA, or both) to detect changes to the distributions of our key business metrics. For instance, we could sample user signups each day and ...
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2answers
144 views

Find degradation rate on a scatterplot

I work for a commercial printing company, and am collecting data regarding the quality of our printing over time (density and dot gains). Essentially, for every job I have a date, a density, and a ...
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3answers
402 views

Advice on a good production level SPC (statistical process control) package?

I am tasked with bringing up an SPC system within our moderately sized, but very technical, manufacturing company. It might be against the rules of this forum, or maybe bad form, to name specific ...
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3answers
166 views

How to verify extremely low error rates

I am faced with trying to demonstrate through testing an extremely low error rate for a sensor (no more than 1 error in 1,000,000 attempts). We have limited time to conduct the experiment so we ...
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0answers
77 views

Calculate quality estimates for distribution of real data

Imagine I have measured heights of humans (in cm) and show the data in a histogram: ...
3
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1answer
494 views

Software for learning statistical quality control

I'm taking a course in Statistical Quality Control as an elective in my masters program. We're using Montgomery's Introduction to Statistical Quality Control, 6th Edition. The book uses minitab ...
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0answers
73 views

What are some quick initial tests to check the quality of a new dataset? [duplicate]

Possible Duplicate: Essential data checking tests When you are presented with a dataset, what are some quick things you can look for to get a feel of how 'good' the dataset is. ('Good' in ...
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2answers
344 views

Understanding statistical control charts

Control charts are all the rage at my company these days. Our "data analysts" (quotes are on purpose) are putting control limits on almost all graphs that they produce. The other day we were looking ...