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Calling All SMEs

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  • #46733

    anon
    Participant

    Dearest SMEs,

    Can you provide me with a reference or general idea behind the importance of degrees of freedom?  Definitions I have, general understanding as to how it affects my statistical outcomes I do not…..thanks!
    F table….how to use and interpret it once I have the f stat? I was raised as a p-value baby and need enlightenment… Thanks again!

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    #154778

    Allthingsidiot O
    Participant

    DoF is  always # of  samples   minus 1
    F table:First  F test  means Fatness in contrast  to  T test  which  means  centering.F test  is  used  when  2  samples variances  are  equal .It  means  to  test for   difference  in dispersion,we  should  calculate   the critical  value  and  the  test  statistic,then upon that  we  can  either ” reject”  or  “fail  to  reject”  the  null  hypothesis.
    Hope it  is  OK now
     

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    #154782

    roadrage01
    Member

    F test likes normality.. alot.  Or better said, F test is not robust to non-normality in the least. 
    Degrees of freedom – How many different types does the test see.  We teach that a minimum of 4 is required in order to use the test.  Higher is better.  It comes down to the noise in the process.  With fewer degrees of freedom, there is more noise that is hidden among the “types” that the test sees.
     
    Hope it helps.

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    #154788

    anon
    Participant

    Thanks RR01,
     
    It sounds like you are describing the number of distinct categories when you describe the DOF…is this correct and if so they are not synonomous, correct?

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    #154789

    SS
    Member

    this trail is the best example of how degenerated this site has become. “f-test relates to fat distribution”, “degrees of freedom have to do with the noise in the process” … you have to really be an allthingsidiot (o) or have roadrage to come up with such utter nonsense … and what does “we” mean, … the totally clueless who failed their baby introduction to statistics … what clowns and bobos!

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    #154791

    Allthingsidiot O
    Participant

    SS
    You  have  stolen  my  explanation in  the  day  light?A  pretender  and  thief in  one unque personality?this  is  really a great mixture.

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    #154799

    annon
    Participant

    Yeah…not exactly what I was looking for….someone with a tad of grey matter want to weigh in here and point me in a direction in terms of references for f distributions….stan, doc, darth, bueller, bueller? 

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    #154800

    qualitycolorado
    Participant

    Anon,I don’t know exactly what questions you are trying to answer, but there are some good free resources on-line that can help you with degress of freedom and the F table.For instance, this page from StatSoft’s statistical textbook discusses degrees of freedom: http://www.statsoft.com/textbook/sttable.html
    … is this kind of reference material you are looking for?
    Best regards,
    QualityColorado

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    #154801

    qualitycolorado
    Participant

    …fyi, the full “electronic statistics textbook: from StatSoft is available (for free!!!) at this website:http://www.statsoft.com/textbook/stathome.html
    Best regards,
    QualityColorado

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    #154802

    qualitycolorado
    Participant

    … also, try searching the “Engineering Statistics Handbook” from the U.S. National Institute of Standards and Technology (NIST) , on-line (at no charge!!) at this link:http://www.itl.nist.gov/div898/handbook/
    I looked quickly, and there are quite a number of references to degrees of freedom — you may find your answers there …
    Best regards,
    QualityColorado

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    #154803

    QuallityColorado
    Participant

    … may also want to try the search engine on the Minitab statistics reference site (also free, even though the Minitab product is not):http://www.minitab.com/Resources/… quite a few hits for “degrees of freedom” … Best regards,
    QuallityColorado

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    #154808

    F test, df
    Participant

    The f-test as you know is based on a ratio of two variances. The idea is that if the variances come from the same population, the two sample estimates of the variances are equal to one (i.e. they are equal)
     
    In the case of the variance estimate you can look at the degree of freedom as the number of sample points that can be varied freely when you know the variance. For example, if you have 5 data points and you know that your variance is let’s say “20”, once you know four data points your fifth data point can be calculated via algrebraic equations. The determination of degrees of freedoms become more complex with more complex designs.
     
    Because you estimate the variances and the ratio of the variances follows an f-distribution you will reject the null hypothesis when the f-value exceeds a critical value. This is in line with the framework of hypothesis testing in general. This critical value is dependent on the degrees of freedom of each of the two samples and the alpha value.
     
    So if you estimate two variances, one with let’s say 5 data points and the other with 7 data points, and you assume an alpha of .05 saying that they are equal you look up the critical value in the f-table and compare it against the value that your two samples show.  The p-value is the cumulative frequency at the point of your estimated ratio given the f-distribution with your specific degrees of freedom. So, you can either look at the p-value or you can compare the calculated f-value with the critical f-value. I hope this helps.
     

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    #154812

    Allthingsidiot O
    Participant

    Excellent  Elaboration,thank  you

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    #154816

    ezweld
    Participant

    Anon,
     SME is the Society of Manufacturing Engineers.
    Degrees of Freedom in Engineering terms refers to Kinematic constraints.
    Three dimensionally speaking an object has 6 degrees of freedom, 3 translational degrees and 3 rotational degrees.
    I doubt your question is regarding the Theory of Exact Constraints, but you really should get your terminology right.

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    #154820

    qualitycolorado
    Participant

    EZWeld,Interesting posting, but come on, cut the guy some slack — he DOES have his terminology right!!Yes, as you point out, while SME can indeed stand for the “Society of Manufacturing Engineers (in the U.S.), its more-common meaning in industry (worldwide) in general is “subject matter experts”. It is quite common to list SMEs on a Six Sigma project charter, for instance.And, yes, while the term “degrees of freedom” does have a specific engineering meaning, it has a specific (and different) meaning in statistics, also — this stastical meaning will be one more commonly referred to in Six Sigma project.
    Best regards,
    QualityColorado

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    #154824

    qualitycolorado
    Participant

    Anon,Here is an another explanation for degrees of freedom:http://www.tufts.edu/~gdallal/dof.htm
    Best regards,
    QualityColorado

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    #154832

    ezweld
    Participant

    QualityColorado,
    Your right, I didn’t even think about “Subject Matter Experts”.
    Every time I see SME I think about Manufacturing Engineers.
     

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    #154834

    Allthingsidiot O
    Participant

    Another  third  concept  for SMEs:Small & Medium Enterprice?

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    #154838

    roadrage01
    Member

    Yes, it would be distinct catagories.

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    #154859

    annon
    Participant

    Thanks to all…links were very helpful QC, along with clearing up the confusion on my acronym. CHeers.

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    #154866

    Bower Chiel
    Participant

    In the UK the acronym SME can mean Small to Medium Enterprise with reference to the size of a business/company!Bower Chiel

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    #154988

    roadrage01
    Member

    Anon, another example of degrees of freedom.
    Shirts come in following sizes: XS, S, M, L, XL (3 degrees of freedom.
    Or shirts sizes 4,6,8,10,12,14,16,18,20,22 (9 degrees of freedom) The increase in distinct catagories reduces the noise by more strictly defining the district catagories.

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    #155102

    Allthingsidiot O
    Participant

    The F distribution has 2 degrees of  freedom,d1 for  the  numerator,d2 for  the  denominator.For  each combination of  these degrees of  freedom there is  a  different F distribution.As the  degrees of  freedom increase,the F  distribution is  less dispersed.In order  to use  the  F table,first  select  the  significance level (Alpha?) to  be  used,and  then  determine  the  appropriate  combination of  degrees  of  freedom.
    good  luck

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    #155126

    Cravens
    Participant

    Try the following link with SME to see how many things SME can mean…
    http://www.acronymfinder.com/

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