# Tagged Questions

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### Control group and bias

I am trying to determine the percentage of patients who will continue to refill a drug on a timely basis. I have data for each month how many patients (as a fraction of those who started the treatment ...
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### Control Limits and Calculating them

This is going to be a very simple question, but I just need to make sure of a few basic things. I'm building some Xbar-R charts and have sample size of 4 and am looking over the Control Limits. I'...
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### How can I check the quality of my probabilities?

I have a data set where the number of accidents are given together with the probability (assumed to be correct) that the number of accidents is less than 4. The task is to calculate the probabilites ...
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### statistical tolerance

My request is: I have data (sums of money) and someone calculated tolerance limits for the data. I want to validate these tolerance limits with statistical methods/arguments. Does anyone know ...
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### Determining if points out of control - non normal distribution

I am trying to create a process in which I can identify if a process is out of control. My idea was to do something similar to 6 sigma, where when a point is outside of the mean by +-3 sigma, then ...
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### standard ways to check data quality?

I have a dataset of tv viewing data (channel, time, # viewers) and want to get some confidence in its quality. What are some standard ways to do this?
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### How well does sample average range estimates sigma?

Suppose there are m subgroups of n items each. The following practice is described by Montgomery in the construction of a $\bar{X}-R$ chart: Let $\bar{R}$ be the average range of the m subgroups. ...
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### Reference to Statistical Control Quality

This semester I'm taking a Green Belt course. I'm really enjoying it and I want to go more deeper in that, I already take this book to start to study Introduction to Statistical Quality Control does ...
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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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### Designing a single sampling plan

I came across the following question: Given, lot size(N), LTPD (lot tolerance proportion defective), consumer's risk and process average. Design a most economical single sampling plan. But, ...
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### Single sampling plan for variables

Please help me understand the following question: Describe a single sampling plan for process average. My confusion: to which of the following plans do the above refer to: Plan 1: plan to control ...
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### Relation between P chart and Chi-square test

P chart checks whether a manufacturing process is in control with respect to the proportion of non confirming items and Chi-square test for homogeneity tests whether several populations are similar or ...
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### What is the mathematically rigorous definition of chunky data?

When in the workplace, certain measurement-taking devices are subject to different numerical accuracy; in some cases, the accuracy can be pretty weak (i.e., to one or two significant values only). ...
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### What is Dodge inspection plan?

What do simply Dodge inspection plan refer to: chain sampling plan, continuous sampling plan or Dodge Romig inspection plan?
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### Probability of failure in a finite population

I regularly inspect finite populations for failures (we make custom products in batches of ~500-800). Currently, we inspect every product for failure, which is quite a bit of work. I want to reduce ...
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### Shewhart and CUSUM control chart for k step ahead forecast error

I am trying to see if the forecast performance has changed over time. I have one to 24 step ahead forecasts. Is it possible to use Shewhart and CUSUM control charts for more than one step ahead ...
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### Where can I find tests that validate the output of popular statistical software? (e.g. R, SPSS, SAS)

This has been difficult to search on Google. I've looked on R's website as well. I assume there are test suites that validate that R, SPSS, SAS, et al are giving the right output for a given analysis? ...
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### multivariate or regular quality control

I want to conduct quality control. Just say the observed variable is X. X consists several indicator variables in it ; X1, X2 and X3. Should I using multivariate quality control method? or combine the ...
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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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### Measurement error in quality

In quality control literature we encounter three terms: Measurement error, Inspection error, Misclassification error. These terms are used interchangeably in different contexts, but I understand ...
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### Statistical Quality Control p-chart

A company manufactures small metal brackets. They are packaged in containers of 1000 brackets each. At the unloading facility, 10 containers have arrived and 36 brackets are selected at random from ...
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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 $$\hat \sigma =s/c4$$ is preferred for UCL and LCL calculations in an x bar chart as it is considered ...
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### distance from normal behaving data with neural network (anomaly detection)

I have a bunch of normal data and I want to use it to build an anomaly detection system. With Multivariate Control Chart or One Class SVM it is possible to obtain the distance of a new sample from ...
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### Z-Chart Control Lines?

Why is the upper control limit 3 and the lower control -3? What's the math behind this? We are converting to a normal distribution and I understand that according to the 68â€“95â€“99.7 rule, showing the ...
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### Oscillations in Sample Size from Type A (hypergeometric) OC Curve

I have two questions concerning the sample sizes obtained from Type A OC curves for single-sample lot acceptance testing. To illustrate the issue, refer to the R code below where the sample size is ...
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### Is there a unified form for Process control and process control analysis

I have done some reading (NIST, JMP, PCS, Juran, some JEDEC, ...) and it appears there are four very common general types of control charts: Shewhart (X-bar, R, S) CUSUM (cumulative sum) EWMA (...
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### I-MR Charts when there is only two observation

I have a data having only two data points (specifically project A and project B). I need to draw an I-MR chart for quality control. Since I have only two points, my graph is not meaningful. How can I ...
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### Control Chart - Descriptive or Inferential?

Which category of statistics do Control Charts fall under? Descriptive, Inferential, or something else? As I'm thinking out loud...Control Charts use elements of Descriptive (central tendency, ...
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### How to calculate False Positive rate?

How to calculate False Positive rate in a scenario where I have 334 bugs in total out of which 57 are Not an Issue type? I believe 57 are false positives in this scenario
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### How find controls limits for CUSUM chart

I am trying to re-do a simulation work in quality control. In this simulation they use bisection search algorithm to find the control limits h (the threshold) that gives the desire average run length ...
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### P-Charts Plot Ratios and Not Proportions?

In P-charts, ratios, not proportions, of defectives over population size are plotted over time. Shouldn't it be called "R" charts instead?
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### When is a single data point enough to be considered a trend in the data?

In the general case, when collecting data points at disparate points in time (such as once per day or two), under what conditions can a single low data point be considered a downwards trend in the ...
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### p-Chart with really tight Control Limits

I have created a process control chart that describes the fraction of deliveries sent to the ideal destination over time. The deliveries all eventually end up at the proper destination, however I am ...
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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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### Quality Control Heat Map

I have data for people about their quality % achieved on a daily basis for last 5 work days, this data is available for one month, say 20 work days. I have worked out the combinations which is 243. 5 ...
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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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### 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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### Control chart constants [closed]

When calculating Upper Control Limit (UCL) and Lower Control Limit (LCL) in control charts I use constants from http://web.uni-plovdiv.bg/kiril/Students/Masters-MYK/table_of_control_chart_constants....
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### Quantifying data completeness in healthcare

In healthcare data, there are often situations when we don't know how complete or incomplete is the dataset for a given patient population. Let's say for example, there are 10,000 patients in the ...
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### How can we say that a clustering quality measure is good?

There are few well known measures like silhouette width (SW), the Davies- Bouldin index (DB), the Calinski-Harabasz index (CH), and the Dunn index . How can we say that a clustering quality measure ...
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### Robust Measures for Forecast Accuracy

I am doing a forecast using robust exponential smoothing methods and to determine / measure the forecast accuracy I want to use robust measurements as well. As I am not really familiar with robust ...
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### Sampling size determination for small probabilities

I am not sure I could find a clear answer on a correct formula for sampling size determination for finding rare events. Specifically I need to be 99% sure, that failure rate of certain population is ...
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### Problems with Outlier Detection

In a blog post Andrew Gelman writes: Stepwise regression is one of these things, like outlier detection and pie charts, which appear to be popular among non-statisticians but are considered by ...
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### Recaculating control limits when an out of control situation is displayed

When plotting control charts if a point plots outside the control limits then the reason for that point to plot outside is checked and if an assignable cause is found to be the cause then after ...
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### Changing a target value that minimize the product being outside the specifications in quality control

I was doing problems in the article here. In the question on page 16 I don't understand part b) how to find a target value that minimize the product being outside the specifications. Can someone ...
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### How to name the concept of the mean shift divided by the standard deviation

In the context of a paper dealing with Statistical Quality Control, I am defining and using the concept of the mean shift divided by the standard deviation of a (normally distributed one-dimensional) ...
### Calculating $\bar c$ in C chart
I am learning a quality control course and in Single sampling scheme for attribute type inspection I don't understand the method used for calculating the values of $n$ and $c$. The method is as ...