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  1. Acer Lambada

    Bias in a chi-square contingency table?

    Hi I am setting up a 7 x 7 contingency table for a chi-square test of independence of forest tree species (below). I want to see where the associations are. But note, for example, that if I want to see the association between red oak and white oak (I suspect there is an important one), I...
  2. Acer Lambada

    Test of just four(4) numbers

    I expected all results to be equivalent. The 326 was an unexpected outlier.
  3. Acer Lambada

    Test of just four(4) numbers

    These are estimates of the total cross-sectional area of wood in a small woodlot according to four different sampling methods. I want to prove the low number is the outlier.
  4. Acer Lambada

    Test of just four(4) numbers

    Hi I have just four numbers and would like to know if there is a stats test that will tell me if one of them does not belong. Specifically, I'm looking at the fourth one (below) and want to prove that it is significantly different from the other three. 715 812 677 326 Is this even doable...
  5. Acer Lambada

    How to calculate degrees of freedom

    Alright thanks for the answer. I'm only glad Excel calculates df automatically in these tests, although I'm troubled that df is not a uniform calculation across all statistics. So my book is fine, and I am more aware now. Learn something new every day.
  6. Acer Lambada

    How to calculate degrees of freedom

    Hi I have a book on statistics that shows two methods to calculate degrees of freedom, depending on the test. 1) For a correlation test it's df = (# rows - 1) - (# columns - 1); 2) for a chi-square test it's df = (# columns - 1) * (# rows - 1). I always thought there was only one way to...
  7. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    That could be done with an increment borer. You take a core sample and count the tree rings. Doesn't damage the tree, still I dunno if the forest preserve district would take too kindly to it.
  8. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    I'm sure it would suit me if I knew anything about Cox and Weibull. I'm still very wet behind the ears in this science. I'll look for your advice when I tackle those two later.
  9. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    Miner: OK good, I seem to be on the right track. I'll see if I can work in standard errors and CIs with the same result.
  10. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    GretaGarbo: you talkin' to me? I'm still trying to get a handle on survival analysis. I'll consult you about Messrs. Cox and Weibull later.
  11. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    Hey I take anything you have to say as important. The techwalla chart just seems a little too simple compared to all the maths I've come across. Maybe in lieu of "Number Died" I should have multiple columns listing causes of death. With that, maybe multiple regression would be a better tool -...
  12. Acer Lambada

    Kaplan-Meier Survival Analysis - advice wanted

    Hi It's hard to find plain-talk on-line instruction in Survival Analysis, so I turn to you all for guidance. Attached is a Survival Analysis table that I gleaned from techwalla.com, and adapted to my fictitious oak forest. Will you please take a look at it and advise me if all is fine, or...
  13. Acer Lambada

    Central Moment - Looking for a definition

    Does anybody have a good definition of "central moment", such as the central moment of a distribution? The definitions I am finding online are all cloaked in mystery. Thanks
  14. Acer Lambada

    App To Find Chi Square sample size

    Hi obh Grande was describing chi-square test of independence when he explained the rules. I assume they apply only to that test. Seems goodness-of-fit tests usually do not have enough contingency cells to apply those rules.
  15. Acer Lambada

    App To Find Chi Square sample size

    Todd Grande makes the following suggestions on sample size: At least 80% of the contingency cells must have an expected value > 5 No cell can have an expected value < 3 Ideal sample size is greater than the total number of cells multiplied by 5
  16. Acer Lambada

    Histograms Reveal Potential Problem

    Your mean of 5 and sd of 16 seems really extreme, but I get the point. Alright I've got a lot of stuff to google here. My next cruise report may have a histogram included. Maybe I'll get a kolmogorov-smirnov test going to determine normality, logarithmic transforms. . . You will probably...
  17. Acer Lambada

    Histograms Reveal Potential Problem

    I think you are saying that the smaller tail will be overrepresented, right? Is 30 samples a sufficiently large sample size to not be concerned about skewed data? Please explain the 95 percentile bootstrap interval. How does that work?
  18. Acer Lambada

    Histograms Reveal Potential Problem

    HLSmith: In all forest cruises I have always gotten reasonable-looking confidence intervals i.e. no negative numbers. BTW VAC is volume per acre.
  19. Acer Lambada

    Histograms Reveal Potential Problem

    As you requested, here are recent histograms: appears bell-shaped appears reverse-J appears reverse-J Pls, hlsmith, I'm interested in what you are saying, but it's a little over my head. Pls make it simpler:confused:
  20. Acer Lambada

    Histograms Reveal Potential Problem

    I would rather stick with my customary reporting. It's what my audience expects, and the method is supported by the textbook. I just want to be sure it's kosher.