# Search results

1. ### 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. ### 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. ### 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. ### 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...
5. ### 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. ### 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. ### 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. ### 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...