Questions tagged [quality-control]
Quality Control relates to statistical methods used for monitoring, maintaining, and/or improving either the statistical quality control of a process or the capability of a process. Use for questions about 6 sigma.
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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 ...
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Quality assurance and quality control (QA/QC) guidelines for a database
Background
I am overseeing the input of data from primary literature into a database. The data entry process is error prone, particularly because users must interpret experimental design, extract ...
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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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Estimating process standard deviation for a quality control chart. What is $s/(c4)$ and how to calculate it in R? [duplicate]
I recently came across quality control charts in my studies and found out that the estimator
$$\hat \sigma =\frac{s}{c_4}$$
is preferred for UCL and LCL calculations in an x-bar chart as it is ...
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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 ...
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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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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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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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Dealing with zeros in a poisson regression
Our code goes through multiple stages of review. I wish to use the number of defects at an earlier stage of review as a "defect density" estimate for later stages.
It sometimes happens that code has ...
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Testing a proportion in an online setting
I work in an online security setting. My goal is to detect if the number of locked accounts per time unit is stable or not. I've tried several approaches, detailed below, but I am not satisfied yet. ...
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Closed formula for D4 constant calculation? (Moving range chart constant)
I need to build a Moving Range Shewhart control chart given a series of observations. In short, I have to calculate the central line and the upper and lower limits as follows
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How can I determine if a time-series is statistically stable?
I have time-series data that tracks the number of sydromics records my organization receives each week. The number of records had been steadily increasing as more organizations started sending us data ...
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Quality control - non-normal distribution
Suppose we have a production line, which makes widgets. Assume also that we know distribution of widget's length ~ $N(\mu, \sigma)$ We measure widget's length and if it is within $\mu+/- 2 \sigma$ we ...
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Using control charts with very large subgroup size?
I am working with a very large data set -- time-series data from an on-line process monitor with a 10 second measurement interval. I am trying to develop control limits for the process using control ...
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t-test with drift in reference distribution
I wonder whether I am behaving correctly with my Student t-test exercise.
I am continuously testing a small data sample of metal-detector antenna readings against a calibration sample distribution.
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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 ...
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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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