Stats Question
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 This topic has 6 replies, 5 voices, and was last updated 14 years, 6 months ago by BritW.

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May 17, 2007 at 7:14 pm #47025
Can anyone help me understand how to get the answer for the following question?
Given the data below and the following requirements: Spec target 0.500. Any rivet must be within + .004. Assume normal distribution. What percentage of rivets is outside lower specification limit?
N Mean Median TrMean StDev SE Mean
100 0.50011 0.50023 0.50013 0.00508 0.00051
0May 17, 2007 at 7:32 pm #156186
veronabillMember@veronabill Include @veronabill in your post and this person will
be notified via email.If you use the raw data, the answer can be determined simply enough using minitab, stat/quality tools/capability analysis / normal nad input the appropriate data columns and sd estimate.
I created a random distribution of 100 numbers using the distribution parameters you supply, and the analysis indicates that about 20.6% of your parts are below the lower spec.0May 17, 2007 at 7:55 pm #156187Would it be possible to determine without the raw data somehow? This question was in some training material but the data is not there.
Thanks!0May 17, 2007 at 8:19 pm #156188Calculate Z for the lower side (Mean – LSL / stdev)
Calculate tail area from Z table.
0May 17, 2007 at 8:50 pm #156191Z=.809
Prob=.3153 or 31.53%0May 17, 2007 at 9:15 pm #156192The calculated zvalue is 0.809. There would be 18.67% below the LSL.
zvalue = (.496.50011)/.00508 or 0.809
Look up 0.809 in the standard normal curve table and you get .1867.0May 18, 2007 at 4:43 pm #156247The formula for Z for a lower specification is:
(MeanLSL)/SD = +.809
P(d) from the Z table is .8133
Z for the upper side is (USLMean)/SD0 
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