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Paired t-test

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  • #43602

    Bec
    Participant

    I have a question about when to use a paired t-test as opposed to a two-sample t-test.  I’ve been given the following information…
    16 pilots have their heads measured to fit new helmets.  All the men have their heads measured once with a cardboard calliper, and then again using a metal calliper.  Determine if there is a difference between the measurements taken using the different callipers.
    I’m not entirely sure that the samples are independent.  Any help would be greatly appreciated…
    Thanks,
    Bec

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    #138533

    Nanni
    Participant
    #138534

    Ken Feldman
    Participant

    DON’T ANY OF YOU DAMN STUDENTS IN THAT CLASS DO YOUR OWN HOMEWORK?

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    #138535

    Bec
    Participant

    Haha.  I’m trying to do it myself (all online, by the way).  All I wanted was some kind of argument or reasonable discussion on how to tell the difference between the two tests, but all I get is people referring me to the text (which I’ve already read, more than once).  It’s not exactly an easy subject to study on your own…  But here’s my argument…
    I think that’s it’s a two-sample t-test.  I think that because we’re examining the difference between the two callipers as opposed to the effect changing callipers has on each subject, the data should be the same regardless of whether we test it on the same people.  That would mean that the samples are independent…
    Any thoughts or suggestions on that??

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    #138546

    JK
    Participant

    The samples are not independant if you are taking the same readings on the same sample with two different gages. I will not provide a reference.  You must do some of your own homework.
    Have you ever checked into Gage R and R?  AIAG has some good examples of a related analysis using ANOVA.
     

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    #138556

    Ken Feldman
    Participant

    You are measuring the same heads with two different measurement devices.  In a 2 sample t test, the heads would be two unique randomly sampled sets of different heads.  Thus a paired t test is preferable since the two sets of data are not independent but share the same set of heads.

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    #138574

    villageidiot
    Member

    Darth, you big softy.

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    #138575

    villageidiot
    Member

    Real quick and not necessarily correct:
    Use the paired t when you have a shared relationship or association between your populations….before and after measures on your process for example….Use the two sample t when you have independent samples…ie no association or realtionship…In situations where your process is going to have some change applied (caliper) and then be measured repeatedly, you use the paired t.  Wait to see if I get rebuked and/or chastised before accepting this pearl of wisdom…good luck and verify.

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    #138578

    Ken Feldman
    Participant

    Welcome back Idiot.  It’s been too long and we did miss you.  Hope everything is OK and your absence was due to being busy and not because you were only allowed outside in the exercise yard an hour a day like Stans.

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    #138580

    Craig
    Participant

    Your example requires a paired t-test since you are not drawing random samples from 2 populations. The experimental units are the same, and you are applying the same treatments to each (measure both ways).  A 2 sample t-test would involve a random selection of pilots for one measurement approach, and another random selection for the second measurement approach.
    I think the independence is related to the pair-to-pair results. In other words, does the difference observed in pair #1 influence the difference in pair #2?
     

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    #138581

    villageidiot
    Member

    Thank you sir!
    Occasionally the gauzy effects of my lithium-prozac-xanex cocktail subside and I am able to spread misinformation and half-truths via our beloved forum…In addition, I have recently re-entered the 6S job market….god help us all…  

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    #138583

    Nanni
    Participant

    JK,
    You said to used paired t-test. And also, you suggest the Gage R&R.
    If you look the AIAG documents, using ANOVA, you DON’T use the ANOVA for paired t-test. You use the ANOVA for independent samples. Actually, a important assumption in the ANOVA is the independency.
    Then, do we have a contradiction ?

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    #138584

    Waskita
    Participant

    DARTH!!! ..I’ve noticed few times that you’re always being rude to pople’s questions but you never actually provide any satisfactory answer nor assistance to the problems.
    What you know is only to post a sarcastic reply, embarasse others asif you’re smart.
    I tell you what, you are the one who is IDIOT who knows nothing about Six Sigma. Thus; you don’t deserve to participate in this forum. A Six Sigma idiot like you plus sarcastic personality makes you deserved to be called “A DUMB-ASS”, Six Sigma Dumb-Ass at least …hahaha

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    #138585

    Charles Hannabarger
    Participant

    Many have taken up the sword against Darth, yet his light sabre still shines on.  If you truly believe he adds no value, I challenege you to go back and revisit his posts.  He, like many here, have an intolerance for those who try to take the easy way out by having others do their thinking and/or research for them.  Indulge in trivial banter at times?  Sure – makes an otherwise “dry” subject more fun and interesting.  Go overboard at times?  In the view of many on the board, yes..  But in the end, through Darth and others on the forum, you have a wonderful resource available to you, if you elarn how to access it.
    Charles

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    #138586

    Pradeep Sharma
    Participant

    I am new to this forum, I had same opinion about Darth what Ferry and others have. But after reading Darth’s earlier posts, I have changed my opinion. He makes dead topic interseting. Now I start by first looking for Darth’s comments.
    Cheers
     

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    #138587

    Anonymous
    Guest

    Ferry.
    I believe the origin of the word ‘idiot’ comes from a greek word ‘idiotes,’  which means ‘layman.’
    Therefore, to call someone a ‘layman’ is hardly an insult. We really ought to raise the ‘insulting’ standards in this forum, along with the standard of some of the questions and some of the answers.
    My favourite insults are to call someone an ‘armchair engineer,’ or an ‘ex-quality engineer’ – especially if they believe Six Sigma is all about defects.
    Cheers,
    Andy
     

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    #138588

    BOAMBB
    Participant

    Ferry Waskita,
    I believe Darth was simply responding to the poster named “villageidiot” (emphasis mine), who has been around for a while.  I do not think the villageidiot minds too much, though I’m fairly sure he’ll respond.
    As others have noted – take a virtual walk through Darth’s posts.  He’s really only offensive to people who do not do their research first…which means I’m really interested in seeing his response to your ridiculous post.
     

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    #138589

    Ken Feldman
    Participant

    Idiot, you know you can contact me offline to discuss career moves.  Always looking for more idiots to join the ranks.
    [email protected]

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    #138590

    Ken Feldman
    Participant

    Waskita,
    I think others have spoken on my behalf, but as Idiot knows, I was referring to him in a familar tone and not insulting just as I have referred to you as Waskita.  Idiot has been posting here a while and definitely adds value and humor.  He has been absent a while and my reference to him was one of friendship, as he knows.  You, on the other hand, need to chill and contribute before you can make any judgements about others.  And yes, I will be rude to true idiots who post nonsense and don’t respect this Forum or its members.  In fact, you fit right into that category.

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    #138591

    Mike Carnell
    Participant

    Ferry Waskita,
    The assistance Darth has provided to people on this website is a matter of record (part of that record is in the preceeding posts that you seem to have selectively ignored). He does provide quality responses and does try to help people and has forgotten more about Six Sigma than most have ever known.
    Maybe you need to backoff an understand what a ridiculous post you have put up.

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    #138592

    Mike Carnell
    Participant

    hacl,
    Nice post. Sooner or later someone will figure out how much experience and knowledge you have.
    In the words of WC Fields “All things considered I’d rather be in Key West.” Well maybe it isn’t an exact quote.
    Regards

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    #138593

    Mike Carnell
    Participant

    Darth,
    Your turn to stir it up? I get back down south and log on for a little late night entertainment and it looked like Julio all over again. I was getting a little teary eyed when I was reading all those posts defending you.
    Your buddy needs to do more than chill. A little zolft  and a some time talking to Mrs. Darth.
    I hope the birthday went well.
    Good luck mi amigo

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    #138596

    Ken Feldman
    Participant

    Mike, welcome back to civilization.  Just because you leave the country for a little while doesn’t mean the crazies stop posting.  We even dragged old Stans out for a bit.  Birthday went well.  Me and the other old geezers at the home celebrated with our favorite prune juice and Don Julio cocktail.  The guys got me a lap dancer but with the consumption of all the prune juice it was mighty uncomfortable.  Then five of us spent 3 minutes trying to blow out the 75 candles.  Mrs. Darth, the jokester, put in a few trick candles and two of the guys had to be rushed to the hospital with shortness of breath.  I got even later and popped a few Cialis with my cocktail and plum wore her out.  Safe travels.

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    #138598

    Waskita
    Participant

    Guess you’re all right.
    Just realized that i might misinterpreted the word idiot which turns-out to be someone’s name which is also supported with my past reading on Darth’s comment on some topic in the past. My apology for that …
    Let’s not make this topic long as i already admit as above ….Cheers

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    #138603

    Mike Carnell
    Participant

    Darth,
    Glad everything went well. It does appear that the extra year has not slowed you down a tad. The wit is still there as well so I assume Mrs. Darth isn’t shipping you off to the old folks home in the near future.
    Regards

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    #138604

    Ken Feldman
    Participant

    Ferry,
    Appreciated and accepted.  Please use that passion and emotion to jump into some of the threads and add to the collective knowledge of the Forum’s SS community.  Thanks and look forward to hearing from you.

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