# Tagged Questions

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### 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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### 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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### 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 ...
154 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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### 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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### Are $\sigma_{70\%} = cte * \sigma /\sqrt{N}$, & $\sigma_{\bar x_{70\%}} = cte * \sigma /\sqrt{N}$ valid with non-normal distributions?

My working population is non normally distributed and from time to time I need to take a sample of it. Sometimes my sample exists of 100 units, at other times of 150 units. Of my sample I calculate ...
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### Color standards for control charts

Are there any references or standards that dictate the color coding of the zones of a Shewhart style control chart. We use green in +/- 2 sigma range, yellow between 2 and 3 sigma and red beyond 3 ...
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### Control Chart Structure - X axis

I am using a computer system with Shewhart control charts. Is it appropriate to use time stamped data as the x axis in a sequential manner. Using this process will create gaps in the control chart, ...
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### Using control charts for data with non-constant mean?

My company would like to use control charts (Shewhart, EWMA, or both) to detect changes to the distributions of our key business metrics. For instance, we could sample user signups each day and ...
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### Advice on a good production level SPC (statistical process control) package?

I am tasked with bringing up an SPC system within our moderately sized, but very technical, manufacturing company. It might be against the rules of this forum, or maybe bad form, to name specific ...
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### Understanding statistical control charts

Control charts are all the rage at my company these days. Our "data analysts" (quotes are on purpose) are putting control limits on almost all graphs that they produce. The other day we were looking ...
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### How would one visualize this data using bar charts?

I am using Google's visualization API for drawing charts that show files downloaded each day. I don't know if this is the best idea, but I am thinking of showing download counts on the Y-axis, ...
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### When controlling a binomial proportion, how to deal with proportions with low confidence?

I'm building a system to alert when the proportion of successes to attempts goes out of control. To visualize the data, I've produced some rolling control charts to get an idea of when things would ...
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### Using geometric mean / geometric standard deviation in statistical process control chart

I am trying to control a binomial proportion that hovers pretty close around 0.1% - 1.0%. Since it seems like dropping from 0.1% to 0.05% is equally as severe as increasing to 0.2% (halving the ...
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### How to calculate the probability for pattern that violates “control chart rules” to occur?

I am going to host a training session to teach healthcare staff how to use control chart (c-chart to be specific), and I need to tell that why these rules (Western Electric Rules) are so called rules ...
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### Given a control chart that shows the mean and upper/lower control limits, how do I tell if the cause of out of control points is assignable or not?

I am given 15 points. The control limits are at +/- 3 $\sigma$. Points 1, 4, 5, 6, 7, 8, 9, 10, 11, 13, and 15 fall within the control limits. Points 2, 3, 12, and 14 are outside of the control ...