The Elsmar Cove Business Systems and Standards Discussion Forums ANOVA for S/N ratio gives different results
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# ANOVA for S/N ratio gives different results

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Post Number #1
4th April 2014, 10:10 AM
 mrbhala Total Posts: 12
ANOVA for S/N ratio gives different results

I am testing paint Film Adhesion. Measuring it in % of portions are peeled off in a test.

When I am saying the quality of paint in terms of Film adhesion, I have to say % of portions NOT peeled off. So % NOT peeled off = 100 - % of Peeled off.

While doing Taguchi analysis
For the first category (% peeled off) I am taking "Smaller is better"
Also I am trying it
for the Second (% NOT peeled off) I am taking "Larger is better"

The results of Analysis of variance
for Means both (peeled off, Not peeled off) gives same R sqr, Adj R sqr and F values
but for S/N Ratio both gives different R Sqr, Adj R Sqr, and F values

Can anyone please explain me Why it is so?

PS: I have attached the data and results.

Thanks
Attached Files: 1. Scan for viruses before opening, 2. Please report any 'bad' files by Reporting this post, 3. Use at your Own Risk.
 Comparison of Adhesion results.docx (13.0 KB, 27 views)

Post Number #2
4th April 2014, 10:30 AM
 Miner Total Posts: 4,185
Re: ANOVA for S/N ratio gives different results

Although you have asked several questions, most can be boiled down to one simple reason. None of your factors are statistically significant (i.e., all p-values >> 0.05). This makes all other numbers irrelevant.

Also, a number of noted statisticians have identified major flaws with the use of S/N Ratios and recommend analyzing the mean and the Ln(StDev) separately. S/N Ratios behave in a non-linear fashion, which can cause the exact problem which you have seen. The Smaller the Better version increases rapidly at first then plateaus. The Larger the Better version increases slowly at first then rises rapidly.
 Thanks to Miner for your informative Post and/or Attachment!
Post Number #3
4th April 2014, 10:55 AM
 mrbhala Total Posts: 12
Re: ANOVA for S/N ratio gives different results

Thank you Miner.
Yes the factors don't have significant influence on the response variables. Actually I am testing 4 variables, out of which 2 are being influenced.

I have question here. I am also done the Gray relational analysis in which for its grades, I did ANOVA. even though the P values are not < 0.05, my guide said I can interpret how much each factor influencing based on the F-Ratio. Is it right?
Post Number #4
4th April 2014, 11:20 AM
 Miner Total Posts: 4,185
Re: ANOVA for S/N ratio gives different results

You can do that PROVIDED that the factors being compared are statistically significant at your designated Alpha risk. I do not recommend doing that with factors that are not statistically significant because you have not disproved the null hypothesis of no effect.
Post Number #5
19th September 2017, 11:58 PM
 yasir ishraq Total Posts: 2
Re: ANOVA for S/N ratio gives different results

Quote:
 In Reply to Parent Post by Miner Although you have asked several questions, most can be boiled down to one simple reason. None of your factors are statistically significant (i.e., all p-values >> 0.05). This makes all other numbers irrelevant. Also, a number of noted statisticians have identified major flaws with the use of S/N Ratios and recommend analyzing the mean and the Ln(StDev) separately. S/N Ratios behave in a non-linear fashion, which can cause the exact problem which you have seen. The Smaller the Better version increases rapidly at first then plateaus. The Larger the Better version increases slowly at first then rises rapidly.
Dear Miner
your post is help full. i have same issue but the mean and SNR give different ranking. i have same insignificant value issue. but my study purpose is to find percentage of contribution only. the two Graphs should be overlapping each other as done in most of the studies.
Post Number #6
20th September 2017, 10:09 AM
 Miner Total Posts: 4,185
Re: ANOVA for S/N ratio gives different results

If your factors are not significant, there is no contribution, it is 100% noise.
 Thank You to Miner for your informative Post and/or Attachment!

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