最近使用Minitab 14 的Capability Analysis 时,发现所生成图中,有几个地方看不懂,请大家指点一下. Observed Performance 中PPM Total 的含义是什么 另外 Overall Performance 的PPM是如何计算的的呢? 请大家多多指点啊!

[ 本帖最后由 victor2008 于 2008-7-3 17:30 编辑 ]

Observed performace:就是通过你的样本估算出来的能力结果
Overal Performace是通过统计分析出来的长期的能力结果

这两者在应用上有什么区别,如果我取一个月的数据进行分析, 这个时候的能力结果应该采用那一个呢? 长期?到底多长为长期呢?

感觉有点模糊,从字面上看,observed是观察到的结果;而overall应该是总体结果;可是不知其内涵.

其实,我们应该善用Minitab自带的help文件,我顺便查了一下,有些信息相信对你有用的.

Observed performance
The number of units in your process output that violate the specification limits. This statistic is based on combined data from all subgroups, so it represents what your customer experiences. The observed performance can be expressed in terms of nonconforming parts per million (PPM) or per hundred (percent

For example, a dairy farm fills 1 gallon milk cartons and you are analyzing the capability of the filling machine. The manager demands a maximum PPM defective of 1900. You produce the following table of observed performance:

Observed Performance

PPM < LSL
10000

PPM > USL
10000

PPM Total
20000


This process has an equal amount of output violating both specification limits, and the total number of nonconforming milk cartons per million is over ten times the goal. The process needs significant improvement.

Note
·    Minitab calculates the observed performance identically for normal capability analysis, between/within capability analysis, and nonnormal capability analysis.

·    If you do not specify a specification limit, Minitab reports a missing value (*) for the PPM exceeding that specification limit.

那是运算时采用的标准差估计不一样而已。