“Np-chart”的意思、由来-开放百科全书

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Np-chart

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{{Lowercase}}{{Infobox control chart
| name = np-chart
| proposer = Walter A. Shewhart
| subgroupsize = n > 1
| measurementtype = Number nonconforming per unit
| qualitycharacteristictype = Attributes data
| distribution = Binomial distribution
| sizeofshift = ≥ 1.5σ
| meanchart = Np control chart.svg
| meancenter =

| meanlimits =

| meanstatistic =

}}

In statistical quality control, the np-chart is a type of control chart used to monitor the number of nonconforming units in a sample. It is an adaptation of the p-chart and used in situations where personnel find it easier to interpret process performance in terms of concrete numbers of units rather than the somewhat more abstract proportion.^[1]

The np-chart differs from the p-chart in only the three following aspects:

The control limits are , where n is the sample size and is the estimate of the long-term process mean established during control-chart setup.
The number nonconforming (np), rather than the fraction nonconforming (p), is plotted against the control limits.
The sample size, , is constant.

References

1. ^{{cite book | last = Montgomery | first = Douglas | title = Introduction to Statistical Quality Control | publisher = John Wiley & Sons, Inc. | year = 2005 | location = Hoboken, New Jersey | pages = 279 | url = http://www.eas.asu.edu/~masmlab/montgomery/ | isbn = 978-0-471-65631-9 | oclc = 56729567 | deadurl = yes | archiveurl = https://web.archive.org/web/20080620095346/http://www.eas.asu.edu/~masmlab/montgomery/ | archivedate = 2008-06-20 | df = }}

2 : Quality control tools|Statistical charts and diagrams

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