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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

    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...
  3. 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...
  4. 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, and adapted to my fictitious oak forest. Will you please take a look at it and advise me if all is fine, or...
  5. 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
  6. Acer Lambada

    Histograms Reveal Potential Problem

    Hi I estimate forest wood volumes by measuring tree diameters and heights in circular forest plots. From these plots I record the volumes then find the variance of the plot volumes, variance of the mean, and standard error which leads me to a 95% confidence interval for the mean plot volume...
  7. Acer Lambada

    Conflicting Results from t-Test and Wilcoxon Signed Rank

    Hi I took before/after measurements of selected tree stems. The distribution looked normal so I used the paired t-Test. The results: test statistic = 1.46 critical value = 1.69 (from table) The instructions say if the test statistic < critical value there is no significant difference among...
  8. Acer Lambada

    Demdromorphometrist wanna meet Waloddi Weibull

    (Dendromorphometry: The sampled measuring of forest trees usually to estimate total forest wood volume.) Hi, Can anyone here give me a primer on the "Weibull distribution"? I know it can be used for estimating the failure rate of things like machine parts. I'm thinking it could also be used...