Blog Archives

Harvesting Canadian climate data

January 14, 2015
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Harvesting Canadian climate data

In December I found myself helping one of our graduate students with a data problem; for one of their thesis chapters they needed a lot of hourly climate data for a handful of stations around Saksatchewan. All of this data was and is available for download from the Government of Canada’s website, but with one catch; you had to...

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Analysing a randomised complete block design with vegan

November 3, 2014
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Analysing a randomised complete block design with vegan

It has been a long time coming. Vegan now has in-built, native ability to use restricted permutation designs when testing effects in constrained ordinations and in range of other methods. This new-found functionality comes courtesy of Jari (mainly) and my efforts to have vegan permutation routines use the permute package. Jari also cooked up a standard interface...

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analogue 0.14-0 released

October 14, 2014
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A couple of week’s ago I packaged up a new release of analogue, which is available from CRAN. Version 0.14-0 is a smaller update than the changes released in 0.12-0 and sees a continuation of the changes to dependencies to have packages in Imports rather than Depends. The main development of analogue now takes place on github...

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Simulating species abundance data with coenocliner

July 31, 2014
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Simulating species abundance data with coenocliner

Coenoclines are, according to the Oxford Dictionary of Ecology (Allaby 1998), “gradients of communities (e.g. in a transect from the summit to the base of a hill), reflecting the changing importance, frequency, or other appropriate measure of different species populations”. In much ecological research, and that of related fields, data on these coenoclines are collected and analyzed in a variety...

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Simultaneous confidence intervals for derivatives of splines in GAMs

June 16, 2014
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Simultaneous confidence intervals for derivatives of splines in GAMs

Last time out I looked at one of the complications of time series modelling with smoothers; you have a non-linear trend which may be statistically significant but it may not be increasing or decreasing everywhere. How do we identify where in the series the data are changing? In that post I explained how we can use the first...

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Identifying periods of change in time series with GAMs

May 15, 2014
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Identifying periods of change in time series with GAMs

In previous posts (here and here) I looked at how generalized additive models (GAMs) can be used to model non-linear trends in time series data. In my previous post I extended the modelling approach to deal with seasonal data where we model both the within year (seasonal) and between year (trend) variation with separate smooth functions....

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Modelling seasonal data with GAMs

May 9, 2014
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Modelling seasonal data with GAMs

In previous posts I have looked at how generalized additive models (GAMs) can be used to model non-linear trends in time series data. At the time a number of readers commented that they were interested in modelling data that had more than just a trend component; how do you model data collected throughout the year over many years with...

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Summarising multivariate palaeoenvironmental data

January 9, 2014
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Summarising multivariate palaeoenvironmental data

The horseshoe effect is a well known and discussed issue with principal component analysis (PCA) (e.g. Goodall 1954; Swan 1970; Noy-Meir & Austin 1970). Similar geometric artefacts also affect correspondence analysis (CA). In part 1 of this series I looked at the implications of these “artefacts” for the recovery of temporal or single dominant gradients from multivariate palaeoecological data....

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Decluttering ordination plots part 4: orditkplot()

December 31, 2013
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Decluttering ordination plots part 4: orditkplot()

Earlier in this series I looked at the ordilabel() and then the orditorp() functions, and most recently the ordipointlabel() function in the vegan package as means to improve labelling in ordination plots. In this, the fourth and final post in the series I take a look at orditkplot(). If you’ve created ordination diagrams before or...

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Summarising multivariate palaeoenvironmental data

December 28, 2013
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Summarising multivariate palaeoenvironmental data

Ordination methods that yield orthogonal axes of variation are often used to summarise the multivariate data obtained from sediment cores. Usually the first or, less often, the first few ordination axes are taken as directions of change or the main patterns of variance in the multivariate data. There is an oft-overlooked issue with this approach that has the potential...

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