Pvalue formula in DOE, Help
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November 1, 2004 at 6:20 pm #37406
I have a pareto of effects graph from a doe, 3 Factor 2 levels
I understand the PValue .05 significance level.
I want to place a formula on the graph to explain how the PValue is calculated. Could someone help me on what the formula would be??
Thanks,
Kathy
0November 1, 2004 at 8:27 pm #110095a
0November 1, 2004 at 8:28 pm #110096Is there a equation for the pvalue?
0November 1, 2004 at 8:40 pm #110097
Ken FeldmanParticipant@Darth Include @Darth in your post and this person will
be notified via email.Which graph are you referring to, the probability plot or the Pareto chart? The value for the p value is the area beyond some calculated value, either Z, t, F or other statistic and depends on the distribution in question. Minitab gives you the value or if you are adventurous, you can look it up in the appropriate table for the statistic you are using. For your DOE, check the values above in the Session Window, assuming you are using Minitab. See if you can’t find some relationship between them and the graphs.
0November 2, 2004 at 1:49 pm #110113Kathy,
What Darth’s saying is right, you have to use the corresponding statistic for which Pvalue you’re looking for (even though the Pvalues are the same for T and F, which they should be).To get the Pvalue for the Fstatistic:P = Fdist(F, df1, df2) where the df1 is the degrees of freedom for the factor of interest, and df2 is the degrees of freedom for the Error term. These dfvalues are shown in the Session Window in MINITAB.
If you don’t have MINITAB then you can calculate the Pvalue using Excel exactly as I wrote in the formula above: = FDIST(F, df1, df2)
What you get is the area (in an Fdistribution) beyond the point which is stated by the Fvalue itself.To get the Pvalue for the Tstatistic:The mathematical relationship between F and T is simply: F equals T^2 (using the single Terms only) therefore there’s no difference between their Pvalues.
I believe you’re using the “Source” as describing your Pareto Chart, so the Fdistribution is your choice (whatever difference that make).
/P30November 2, 2004 at 2:07 pm #110114Thanks for the help guys. I understand it better now.
Kathy0 
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