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    fiting a model to data with two peaks (bimodal?)

    I have plant growth data dependent on temperature on a yearly basis for 6 years. The data exhibit two 'peaks' in growth during the season, with a dip in between. Individually, the yearly data does not appear to be normal using a probability plot. But when the data is collapsed into one column...
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    Plotting the pdf of a negative binomial distribution using mean and stnd deviation

    I have been using a negative binomial distribution to describe my data; in order to allow me to randomly sample from the parameterised distributions. I have had no problems getting r (the number of successes) and p (the probability of success) for my distribution. My problem is that I would like...
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    comparing linear models to test for statistical similarities

    I am trying to describe plant growth over time using accumulated temperature (dd) as my independent variable and the plants 'growth stage' (gs) as my dependent variable. The shape of the data is sigmoid and I have three different sets of data for different geographic areas. I decided to use a...
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    comparing regression coefficients between different models to see if they are similar

    Hi all; This is a very elementary problem; but unfortunately, my strengths do not like in statistics: I am trying to describe plant growth over time using accumulated temperature (dd) as my independent variable and the plants 'growth stage' (gs) as my dependent variable. The shape of the...
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    I want to split a column of data into stastically significant groups

    I want to split a column of data into stastically different groups I have a column of average annual temperature data. According to theory, whether the temperature is very cold or very hot (or moderate) it will have an effect on a species that I am interested in. So what I want to know, is if...