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18 views

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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46 views

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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7 views

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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31 views

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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14 views

interpretation after sample decreases due to extra control variables

I have run some logistic regressions and are now busy with interpreting the results. When I add two extra control variables to my regression, the total amount of observations is decreased with almost ...
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0answers
21 views

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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19 views

Which type of control chart should I use?

I have a data for voice traffic of one week. Traffic measured at every hour. So according to this data i need to define the control limits (UCL and LCL) using R. Which type of chart should I use.. I ...
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0answers
19 views

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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33 views

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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1answer
48 views

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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2answers
65 views

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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0answers
35 views

Control chart constants [closed]

When calculating Upper Control Limit (UCL) and Lower Control Limit (LCL) in control charts I use constants from ...
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46 views

Can a classification algorithm be used to measure the Clustering Quality (CQM)

Can a classifier be used to measure the Clustering Quality measure? I have come across this paper where the researcher uses a classifier like : five nearest neighbor classifier, a C4.5 decision ...
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42 views

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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39 views

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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0answers
51 views

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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0answers
40 views

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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64 views

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-statisticans but are considered by ...
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0answers
14 views

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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34 views

C chart control limits

Can someone please help me to do this problem: A C Chart for non-conforming units is set up with lower control limit $0$ and a center line at $\bar c$. The upper control limit (UCL) for this ...
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0answers
24 views

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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88 views

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) ...
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0answers
38 views

How to determine if a U chart or a C chart to be used

This is regarding theory of attribute type control charts.In a question it is given data for the number of non confirmities per 1000 meters of wire. I have to calculate control limits for a ...
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0answers
23 views

Calculating $\bar c $ in C chart

In studying C chart I came accross this problem in Statistical Process control by Douglas .C.Montgomary. In this exercise it says: A control chart is used to control the fraction of non ...
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20 views

Area of Opportunity in C chart and U chart

In the article whether to use C chart of U chart is determined by area of opportunity.But I don't understand what is meant by area of opportunity and how it relates to C chart and U chart.Can ...
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65 views

Finding n and c in single sampling plan

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 ...
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0answers
174 views

Calculation of Average run length in non-normal distribution

I want to calculate Average Run Length(ARL) in non-normal distribution. In a normal distribution, I can calculate the ARL for example, ...
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19 views

Monitoring high quality near zero defect processes

What are the latest techniques for monitoring discreet defects in high quality processes with defective rates in the parts per million range?
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1answer
56 views

Control limits in $\bar{x}$ and R chart

I am learning a Quality Control course and in theory part I don't understand calculating the control limits for $\bar{x}$ and R chart.I want to know, say when I calculate the R chart control limits no ...
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0answers
14 views

How to get the improvement index in monthly basis for employees absence

I have the following information for each month of the year: Total Absence Days in a given month Total Headcount in a given month I want to get an index in which I can compare months and see if ...
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0answers
117 views

Detecting a trend to increase, in a time series, in real time

Probably, someone who's into technical analysis of share prices eats stuff like this for breakfast. Me, I couldn't devise a theoretically acceptable approach. I have this thing (private working set, ...
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1answer
52 views

Use daily production as a check on whether monthly production goal is likely to be met

This is a real small business problem, not a homework problem. A monthly production goal is 60000. We want to be sure that say 95% of months meet this goal. The goal is a minimum, so we want to be ...
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1answer
120 views

Quality Control Chart for non-normal distributed data

I am interested in building quality control charts for time series data where every data point has different gradation within the range of 0 to 1. For example first data point X1 may be 0.1, 0.2,..,1 ...
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2answers
4k views

What is “the” correct way of calculating Cp/Cpk values for Statistical Process Control?

There seems to be many different methods of calculating Cp/Cpk values in SPC, and I need help in determining which one to use at any given situation. Currently, we need to show Cp/Cpk values when ...
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1answer
104 views

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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0answers
65 views

Mean number of samples before out of control in p-chart

I'm stuck with this problem on quality control and p-charts. There is a given process, monitored periodically taking samples of 100 items each and counting the number that are defective. In the last ...
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2answers
163 views

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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2answers
787 views

Why isn't bayesian statistics more popular for statistical process control?

My understanding of the bayesian vs frequentist debate is that frequentist statistics: is (or claims to be) objective or at least unbiased so different researchers, using different assumptions can ...
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1answer
167 views

On properly setting up a control chart

Let me present to you the way I have being 'doing' control charts up until now. I have a series of $k$ samples of size $n$. I calculate the the sample means $\bar{x}_i$ and the grand mean ...
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1answer
330 views

Control charts of seasonal data

I have been asked to develop control charts for my company - or some other means of quickly identifying when ticket sales are "out of control" and not just a random blip. The data we are looking at ...
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1answer
40 views

Control lines that converge?

I'd like to have some control lines that converge, if the random variable observed becomes stable. For example, as the chart below, the variable starts at around 3.0, the upper control line is around ...
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2answers
142 views

Meta analysis: How to assess the quality of each of the individual studies in a systematic way?

I have a meta analysis at hand. I have reported on the quality of the included studies in a narrative form. But after I was requested about "quality assessment". I guess it might be something else, a ...
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130 views

Sampling for quality control

I would like to do some quality control study for a set of manufactured components. For a given set, I can draw several samples. Each drawn sample can be either good or bad. My plan is to create a ...
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2answers
77 views

Method to remove bad values in time series (bad values known to take on a particular value)

This sounds easy, but I don't know of a good statistical method for it. I have a time series that has (good) data points that range from ~3.5 to 30. The data are collected by an automated sensor. ...
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0answers
45 views

Non-Analytic extrapolation

I have some samples of a stable real-world process. Its is polymodal, and does not cleanly fit any of the "textbook" analytic distributions. I need to make very accurate estimates of the maximum ...
2
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1answer
367 views

Bootstrap USL/LSL for non-normal data

This is new statistics space for me, so please excuse my ignorance. I have some data (N=180) that isn't normally distributed (verified in Minitab, P<0.005) and I want to use the data to get a +/- ...
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1answer
3k views

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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0answers
416 views

Control chart Xbar and R missing values

I am taking a business statistics course and I can't seem to figure out how to find the missing figures in the following problem; here's the question: Using the data below, determine the trial ...
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2answers
178 views

Data analysis on multiuser environment

I have following environment that I'd like to analyze. My company is divided in two teams: Insert Team (composed by 150 persons) Quality Check Team (composed by 10 persons) Suppose that all ...
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0answers
40 views

Software quality control references

I'm looking for references on statistical quality control of software. My searches have turned up a lot of writing on how to predict the time that software projects will take, and also software ...