Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
0answers
9 views

Product Yield in Capability Analysis

I couldn't find a 6 sigma tag so please let me know if this is posted in the wrong forum. I'm performing a capability analysis on a manufacturing process. However my process output is Pass/Fail. This ...
0
votes
0answers
6 views

Dealing with low-resolution sensors for SPC

I want to apply SPC to a data stream coming from a sensor, but the resolution of the sensor is very low. It measures the temperature as an integer, and is almost always at 290 degrees, with a couple ...
1
vote
0answers
8 views

Which control chart can use for monitoring of covariance matrix of cofficient?

I have a series of panel data, which includes p cross section and t time. I estimated the covariance matrix of coefficients for periods for periods. Now my data includes the individual period and the ...
0
votes
0answers
9 views

Average of counts - which control chart to use?

I have data coming from a lab. Each test examines how many bacteria units are in the lab (counts). The examination was done 3 times a day, during a period of 16 days. The quality specifications of the ...
0
votes
0answers
143 views

AQL vs AOQL Sampling

What is the benefit of switching from a sampling plan based on AQL to a sampling plan based on AOQL? I believe I understand the definitions of each, such as stated here, but I do not understand the ...
0
votes
0answers
24 views

Schewhart X-bar Chart: Disadvantage of using subgroup of size 1?

I understand the correct procedure for creating X-bar charts but find myself wondering where the disadvantage stems from in reducing the subgroup size from 4 or 5 down to 1. I would think that if I ...
0
votes
0answers
6 views

Control Limit Estimates: How are subgroups utilized in univariate data?

I see a lot of mention of subgroups when reading about control limits but am wondering how they're supposed to be utilized. E.g., if a factory produces widgets and wants those widgets to sustain a ...
0
votes
0answers
13 views

IMR / Shewhart Charts and Missing Data?

I've been asked to modify a set of IMR charts so they 'show' lots with missing data. I'm interpreting the request to mean display the lot on the X-axis with other lots and somehow leave a gap in the ...
1
vote
1answer
29 views

What is meant by subgroup?

I am learning about control charts but I am unable to wrap my head around the concept of subgroups. What are subgroups? I understand that they are group of homogeneous data, but why do we need to ...
0
votes
0answers
13 views

Identify whether my NEW data is having some new pattern(s) or trend(s) from the OLD data in REAL time

After going into production the model starts predicting in Real Time. Therefore it becomes the need to handle the scenarios that may arise in Real Time. If we are planning to use the REAL TIME data ...
0
votes
0answers
5 views

Identify whether my NEW data is having some new pattern(s) or trend(s) from the OLD data

After going into production the model starts predicting at Real Time. Therefore it becomes the need to handle the scenarios that may arise in Real Time. If we are planning to use this data for ...
0
votes
0answers
12 views

Comparing Distributions - Continuous Predictor with Binomial Response

I am trying to determine whether there is a statistical difference between a samples distribution to a known population. The predictor is velocity, and the response is Complete Penetration/Partial ...
0
votes
0answers
8 views

Is there a systematic behaviour/change?

don't know how to call the title so please excuse the rather general naming. I've a lot devices and each has it's own specific voltage which I've histogrammed. After the same treatment (meaning, each ...
0
votes
0answers
39 views

Data transformation and tolerance intervals

I need to construct tolerance limits for some data. I am doing the next approach: I have n data points I transform the data to normal data using a Johnson transformation. I compute the desired ...
0
votes
0answers
6 views

Area between upper control limit and mean… Is it meaningful?

I'm trying to come up with a metric that assesses the general "health" associated with some system. I don't have the right data calculated to come up with a classification model or anything like that. ...
0
votes
0answers
34 views

Judging when to use Individual moving range control charts vs X-bar S or R control charts for subgroups?

I obtain temperature data every 30 minutes for 6 hours or so. I want to chart this data for trends, special causes etc for 80 similar instances. I've read that if the reading is over a single ...
3
votes
0answers
40 views

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. ...
0
votes
0answers
196 views

Johnson Transformation Inverse

I am using the Johnson package in R, I need after the Johnson transformation do some inference using the results of Normal distribution, after that I need to go back to the original data. I have ...
0
votes
0answers
10 views

Calculating standard deviation from succesive differences identifies inherent versus externally caused variation?

I am reading Six Sigma For Dummies by Gygi and Williams, 2012. In the book (chapter 9, page 125) it says that calculating standard deviation by taking the average of the absolute successive ...
0
votes
0answers
9 views

Runs indicating a trend in statistical process control?

Suppose I have a factory machine that outputs widgets. They are supposed to be all the same weight, but in reality fluctuate slightly in weight from widget to widget. This fluctuation could be random, ...
1
vote
1answer
102 views

Non-normal distributions vs data transformation

How would an individual decide on treating Non-normal data for, e.g. control charts; data transformation vs Non-normal distributions such as Weibull? I have access to Minitab but the decision point ...
0
votes
1answer
43 views

XmR Chart Control Limits - Why Moving Range - Why Not population 3sigma

Why do we compute the control limits for the individuals or XmR chart with an estimated sigma, 2.66 x mR(avg)? I understand that the overall population sigma is different. But why is one more ...
1
vote
1answer
40 views

If the population size was large enough that the sample size required to represent it is too large to be practical, what should be done?

i just started working as a quality control engineer at a poultry company, one of my first duties is to design a mechanism to ensure the quality of the end product (the Chick) and processes leading up ...
1
vote
2answers
60 views

How to calculate reliability (or confidence of no more errors) after a large run with no errors?

I have a (software) system which was failing, with a particlular failure mode, about 0.5% of the time. This was low enough that it was not noticed during inital development. After performing several ...
0
votes
1answer
86 views

monitoring variation for a process with a non-constant average

We use control charts in our lab to monitor process variation, and I'm trying to reconfigure the chart for one of our methods, so data is better represented. For the method in question, we use a ...
1
vote
0answers
48 views

teaching over-calibration (from process control) to non-stats folks

When I took my courses in process control, they talked about "over-calibration", which is repeatedly tuning a process to attempt to reduce natural cause variation, as something that increased overall ...
0
votes
1answer
26 views

SPC - do the Nelson rules change if the control limits are changed from the “default” of 3 standard deviations?

I am aware that, in SPC, one can theoretically chose different control limits based on the number of standard deviations one wishes to use. If one uses a control chart with control limits with fewer ...
2
votes
0answers
54 views

Is it possible to use statistics to detect a rising temperature scenario?

It is required to monitor temperature data from a manufacturing environment. The particular use case is to detect if the temperature is rising beyond normal values to enable timely corrective action. ...
1
vote
0answers
30 views

Validating my thinking

I'm pretty sure I'm seeking standard deviation and finding the mass of my 'widgets' that exist outside my SD. Here's the context. I just sorted a bunch of widgets into two piles. One pile is known ...
1
vote
1answer
42 views

Detect statistically significant decrease in event rate

Pardon the novice question, but I really don't know what I'm supposed to be searching for on this one. I am monitoring a system for raw events. I can identify the "type" or "kind" of an event, but ...
0
votes
1answer
912 views

X-bar R charts with varying subgroup size

I am using control limits to check if a process is going out of control or not and detect the mean shifts over time. I am aware of how to apply the control limits, but not really sure about the ...
1
vote
1answer
121 views

Is there a Status Machine Chart?

I find this type of chart quite often, but I don't know if it is known by another specific name: It looks like a 100% stacked bar chart, but colors repeat and it is actually different. It may be ...
1
vote
0answers
40 views

Estimating a tail probability based on the sample mean and standard deviation

I want to know if a sub-population has the same upper quantile as a parent population. Assume that in the parent population, proportion $1-\alpha$ of the data lies below threshold $k$. I can observe ...
2
votes
0answers
144 views

Poisson Distribution Process Control Limits

I am measuring the number of events that happen within n minute intervals for a group of 100 stores. My problem is, I am looking for a way to calculate a threshold for the acceptable number of times ...
2
votes
1answer
51 views

Nelson Rules - what if points are only just on one side of the mean?

This question relates to the Nelson rules for statistical process control. Does rule 2 - nine points in a row on the same side of the mean - apply if one or two of those points are very narrowly on ...
0
votes
1answer
92 views

Control limits for Xbar chart

I am flirting with the idea of using econometrics and regression to improve upon the classical SPC control charting techniques. Hopefully with the end of goal of doing trend analysis on mean and ...
0
votes
1answer
31 views

Quasi-experimetal Research is it necessary a control group?

A short-term entrepreneurship course is gonna be implemented in one city in 10 schools. I would like to stablish a quasi-experimental research in order to measure the impact of this course on skills, ...
6
votes
2answers
218 views

“Random variable” vs. “random value” (when translating from Russian into English)

In the introductory part of a Russian document I was translating, there was a simplified description of a control chart-based quality management system. The description contained this sentence in ...
1
vote
1answer
392 views

Statistical Quality Control Data Gathering

Data has been gathered for a specific analytical test method to start SQC. The issue is that when the data is tested for normality, using Anderson Darling, the null hypothesis can not be rejected. -...
1
vote
1answer
28 views

How to find the time to failure of a component using mean failure time

Is there a way to find the time it will take a component to fail if we know the average failure time. For example a bulb has a mean failure time of 100 hours but is working even after 200 hours. Can ...
1
vote
0answers
221 views

Imputing missing values and quality control of hourly weather data

I have hourly weather data for a number of weather stations in radius of some 300 kilometers, for second half of the last century. Missing values range from few hours to a whole month. I am working ...
0
votes
0answers
450 views

Why is Bayes Success Run Theorem independent of total “population” size?

In Bayes success-run theorem (below), total "population" size is not a parameter. Why is this? $$R = (1-C) ^{ (1/n)}$$ where: $R =$ Reliability (or probability of success), $C =$ confidence level, ...
3
votes
1answer
387 views

One-class KNN for Quality Control

I've come across this paper https://uta-ir.tdl.org/uta-ir/bitstream/handle/10106/1827/Sukchotrat_uta_2502D_10083.pdf?sequence=1&isAllowed=y] where it is described a k-Nearest Neighbors Data ...
0
votes
0answers
19 views

Control Chart factor $c_4$

I have found several authoritative sources with differing methods for calculating the control chart factor $c_4$. Are these methods truly equivalent, and if they are not, which method is the "real" ...
0
votes
2answers
51 views

Applying Sample Sizing To Performance Monitoring?

Let's say you have a machine that runs on an algorithm with inputs that can be modified. Every 3 months, that machine produces 40,000,000 widgets. You can monitor if the widgets are being made ...
1
vote
1answer
58 views

Comparing new data with old data

I have a use case where I need to check if new data received this week, is different from older data received last week. The data is continuous (basically voltage & power readings from a machine). ...
0
votes
0answers
27 views

Finding the parameters (n,c) and (N,n,c) in single sampling plans

I'm learning about devising single sampling plans for quality control, and I'd like to learn how to solve for the key parameters. Specifically, I have two related questions. Suppose my boss ...
0
votes
1answer
81 views

Control charts constants computation

The various control char constants are usually given for various population sizes, often up to 25. I'd like to have more flexibility; is there à way to compute those instead? Thanks
1
vote
0answers
3k views

Understanding Defect Rate of Manufacturing Process

(NB: I don't have a very strong background in statistics, so I would not be surprised if this question is naive or the answer is apparent from some rather basic principle.) I'm wondering how I might ...
4
votes
0answers
170 views

How do you evaluate machine learning model already deployed in production?

so to be more clear lets consider the problem of loan default prediction. Let's say I have trained and tested off-line multiple classifiers and ensembled them. Then I gave this model to production. ...