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.
195 questions
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Role of Z-Tests in Kernel Density Estimation for Cluster Classification
In a recent bioinformatics paper, the authors describe a statistical/machine learning approach to classify clusters of cells using kernel density estimation (KDE) and Z-scores. While the details of ...
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Is this a sound way to apply Bayes’ rule to track confidence in process improvement over time based on observed progress (given the assumptions)?
Problem We're trying to improve our defect detection system in a manufacturing process over the course of a year. The goal is to gradually increase the percent of defects caught earlier in the process....
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Testing if observations in repeated measurements show a consistent order?
I have to analyze a biological dataset. Let me describe the experiment and data first: We have a piece of plastic with hundreds of wells where chemical/biological ...
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What is the difference between Tolerance Interval and Control Limits?
I understand that a tolerance interval indicates a range within which a specified percentage of a population (future value) is expected to fall. Control limits, on the other hand, represent the ...
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Should I calculate the average over all values or at each point in time to analyse?
I am trying to analyse maintenance costs of different models of cars over time. I have many models. Some sample data for a model looks like this. For example this could all be for Ford cars and each <...
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Rejection of samples suspected of not coming of the target population
Say, there is a stationary process that should resemble a Gaussian distribution with 'known' mean and variance. Iid samples in triplicates (or n-plicates) are taken from it. It is also known that ...
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Hotelling's $T^2$ chart for subgroups with unequal size
I have been reading about Hotelling's $T^2$ control charts and I'm unsure on how to deal with the case where the mean observations come from unequal-sized subgroups. Consider $m$ observations $\mathbf{...
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2 votes
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Correct setup for a Bayesian gamma model
I am interested in understanding how center volume affects a quality metric in a healthcare application. Each program's performance is reported as an observed/expected (O/E) ratio where the expected ...
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3 votes
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Within-group and between-group variation in real life processes?
In the context of Statistical Process Control (SPC), control charts are used to monitor a process over time and detect shifts in the mean or variation. The traditional Shewhart $\bar{X}$ charts makes ...
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How to statistically discover significant process change effectiveness?
I am currently working on a project where I need to assess the effectiveness of changes made in a production process. Our initial success rate was 50%, and after making some alterations, we've ...
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Single control limits for process with various subgroup sizes
I have a production process, which produces one or more goods on a certain day. For this example, assume the weight of the produced good is consistenlty measured. However, the operators can ofcourse ...
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1 vote
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Statistical Approaches for Interpreting Weekly Changes in a Percentage Metric
Overview Each week we have some number of trials and successes, and we track the percentage of successes each week, this is our metric. Made up example: A loan company - each week we get some ...
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Different methods to calculate standard deviation
I am doing a study using Statistical Process Control and have to calculate the standard deviation. I am aware of a number of ways to do this. The first method is using the sum of squares (classic ...
LabMat
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The link between AQL, RQL and the reliability of a process
The problem is to distinguish between the definitions of AQL, RQL and reliability in the field of quality control. Let us just pose the context. We wish to calculate the reliability of a manufacturing ...
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Does the rules "7 or more consecutive points on one side" in Statistical Process Control take in account the amount of data point?
I'm reading on Control chart rules and there is a rule which says: "7 or more consecutive points on one side" in considered "out of control". However, does it take into account the ...
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