# 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.

175 questions
Filter by
Sorted by
Tagged with
1 vote
39 views

### 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 ...
12 views

### How to calculate the process control limits when there is not much data left?

Context: To compute the "Process Control" limits, I am following the Stacey Barr's blog. My question: After detecting the signal, if I don't have enough data points left in my dataframe, for ...
1 vote
100 views

• 311
1 vote
21 views

### Find control chart limits based on existing data

I'd like to produce a control chart that tells me if a given process will be within bounds in the future or not. Currently, the process gives me simple timeseries data, per minute ...
• 121
1 vote
239 views

### Hotelling T squared seemingly useless at detecting a mean shift

I am trying to develop a single-sample Hotelling $T^2$ test in order to implement a multivariate control chart, as described in Montgomery, D. C. (2009) Introduction To Statistical Quality Control, ...
• 311
65 views

### statistical process control for non normal time series

Let us say I have several KPI measurements per month. There may be different numbers of measurements per month but there are more than 30. The monthly distributions do not look normally as shown in ...
• 2,245
1 vote
70 views

### XmR charts for several measures at the same day/month

Xmr charts are often used in statistical process control (see for example). They make sense, but I wonder what one does, if one has several measure per day/month etc. Should one just use the average (...
• 2,245
1 vote
27 views

### Setting limits for process control of low probability error

I have a process which produces plastic parts. I have a requirement that states that the weight shall be > x grams. So far I have measured each individual part produced (around 250 pieces) and ...
59 views

### How to find value of omega in CUSUM?

I am trying to understand CUSUM or Cumulative Sum Control Chart. In the example on above linked Wikipedia page, the formula for high CUSUM value indicating positive ...
• 10.1k
77 views

### Using an old trained model on a new data - comparing two populations

I have two populations with the same set of features. The range of the features' values is also the same. I trained Random Forest Algorithm on the first population. Thus, I wonder whether or not I can ...
• 103
1 vote
339 views

### Can CUSUM be used to detect anomalies in clustered data?

I am looking at approaches to detect anomalies in network traffic in terms of packets being sent with a very short inter-arrival time (IAT). Said differently, the longer (possibly) uniform IATs would ...
200 views

### What do the letter and the subscript in the Shewhart's control chart constants ($A_2, A_3, c_4, c_5, \ldots$) mean?

The expected value of the sample standard deviation is $$E(s) = c_4(n)\sigma$$ where $$c_4(n) = \sqrt{2\over n-1}{\Gamma({n\over2})\over\Gamma({n-1\over2})}$$ The page on Wikipedia led me ...
• 566
452 views

### Find a single-sampling plan for which $p_1=0.02$, $\alpha=0.01$,$p_2=0.06$ and $\beta=0.10$

I am not sure where to start. My previous lecture gave very limited information on what to do here, so my current toolbox only consists of these formulas: 1-\alpha=\sum_{d=0}^{c} {n \choose d}p_1^d(...
• 447