Statistical Analysis Stack Exchange
Statistical Analysis Stack Exchange

Questions tagged [control-chart]

One of the key tools of process control.

The purpose of a control chart is to characterize how well a process is staying within stable and targeted behavior and alert in a timely manner when it has departed from it.

NIST link on process control tools: http://www.itl.nist.gov/div898/handbook/pmc/section1/pmc12.htm

The NIST pages on Control Charts are here: http://www.itl.nist.gov/div898/handbook/mpc/section2/mpc221.htm

Here is a text on the subject: http://people.irisa.fr/Michele.Basseville/kniga/

24 questions
10
votes
5 answers

How to interpret a control chart containing a majority of zero values?

I am using a control chart to try to work on some infection data, and will raise an alert if the infection is considered "out of control". Problems arrive when I come to a set of data where most of the time points have zero infection, with only a…
lokheart
  • 2,999
  • 7
  • 37
  • 47
8
votes
4 answers

Given a control chart that shows the mean and upper/lower control limits, how do I tell if the cause of out of control points is assignable or not?

I am given 15 points. The control limits are at +/- 3 $\sigma$. Points 1, 4, 5, 6, 7, 8, 9, 10, 11, 13, and 15 fall within the control limits. Points 2, 3, 12, and 14 are outside of the control limits, with 2 being below the lower control limit and…
Thomas Owens
  • 1,091
  • 1
  • 10
  • 19
7
votes
2 answers

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 at some graphs of calls into our support call…
Dave Kincaid
  • 1,458
  • 1
  • 12
  • 18
5
votes
2 answers

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 companies, although if anyone is comfortable doing…
Mike Williamson
  • 432
  • 5
  • 16
4
votes
1 answer

How to calculate the probability for pattern that violates "control chart rules" to occur?

I am going to host a training session to teach healthcare staff how to use control chart (c-chart to be specific), and I need to tell that why these rules (Western Electric Rules) are so called rules that when pattern is matched, outbreak can be…
lokheart
  • 2,999
  • 7
  • 37
  • 47
4
votes
2 answers

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 = $(1-p^k)/(p^k (1-p))$?
Harry
  • 1,107
  • 9
  • 24
3
votes
1 answer

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 $\bar{\bar{x}}$ --- the mean of the sample means (or the mean…
JP McCarthy
  • 237
  • 2
  • 9
3
votes
2 answers

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 sigma. I am hearing that using green, yellow and red…
Rodger Ziolkowski
  • 31
  • 2
2
votes
1 answer

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 are seasonal with a positive trend (sales revenue).…
Hal Baggot
  • 21
  • 3
2
votes
1 answer

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 6.0, and lower control line is about 2.0. At the…
athos
  • 389
  • 3
  • 16
2
votes
1 answer

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 +/- 4 sigma specification limit. Basically, I want to…
AHartman
  • 21
  • 1
2
votes
1 answer

How to interpret a control chart containing a majority of zero values? (Part 2)

(I know it is not quite appropriate to quote it as "part 2", but since the question has been dormant for quite a while, I hope by doing this will rise peoples' attention again, you may have a look of part I here.) I have come across an article…
lokheart
  • 2,999
  • 7
  • 37
  • 47
2
votes
0 answers

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 50 samples we found a total of 622 defective…
emain90
  • 21
  • 2
1
vote
0 answers

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 value for a number of samples that is much larger…
EngrStudent
  • 8,232
  • 2
  • 29
  • 82
1
vote
1 answer

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 the mean, $\mu$, and with bootstrapping I…
siegfried
  • 469
  • 1
  • 5
  • 4
1
2