256 search results for "Anova"

Assessing the Forecasting Ability of Our Model

September 2, 2011
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Assessing the Forecasting Ability of Our Model

Today we wish to see how our model would have faired forecasting the past 20 values of GDP. Why? Well ask yourself this: How can you know where your going, if you don't know where you've been? Once you understand please proceed on with the following post.First recall the trend portion that we have already accounted for:> t=(1:258)> t2=t^2> trendy= 892.656210 +...

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Major changes to the forecast package

August 25, 2011
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Major changes to the forecast package

The forecast package for R has undergone a major upgrade, and I’ve given it version number 3 as a result. Some of these changes were suggestions from the forecasting workshop I ran in Switzerland a couple of months ago, and some have been on the drawing board for a long time. Here are the main

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Z-Tests: Should we even bother?

August 23, 2011
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Z-Tests: Should we even bother?

Should statistical teachers continue to teach z-tests?vote:  save z-test, or stop z-testLooking at textbooks, articles and general research I cannot remember the last time I saw someone use a z-test in a study. I have seen many a t-test, ANOVA, ch...

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Model Validation: Interpreting Residual Plots

July 18, 2011
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Model Validation: Interpreting Residual Plots

When conducting any statistical analysis it is important to evaluate how well the model fits the data and that the data meet the assumptions of the model. There are numerous ways to do this and a variety of statistical tests to evaluate deviations from model assumptions. However, there is little general acceptance of any of the statistical tests. Generally...

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The foundations of Statistics: a simulation-based approach

July 11, 2011
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The foundations of Statistics: a simulation-based approach

“We have seen that a perfect correlation is perfectly linear, so an imperfect correlation will be `imperfectly linear’.” page 128 This book has been written by two linguists, Shravan Vasishth and Michael Broe, in order to teach statistics “in  areas that are traditionally not mathematically demanding” at a deeper level than traditional textbooks “without using

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Additive modelling and the HadCRUT3v global mean temperature series

June 12, 2011
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Additive modelling and the HadCRUT3v global mean temperature series

Earlier, I looked at the HadCRUT3vgl data set using generalized least squares to investigate whether the trend in temperature since 1995 was statistically significant. Here I want to follow-up one of the points from the earlier posting; namely using a … Continue reading →

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Additive modelling and the HadCRUT3v global mean temperature series

June 12, 2011
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Additive modelling and the HadCRUT3v global mean temperature series

Earlier, I looked at the HadCRUT3vgl data set using generalized least squares to investigate whether the trend in temperature since 1995 was statistically significant. Here I want to follow-up one of the points from the earlier posting; namely using a statistical technique that fits a local, and not global, model to the...

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Global warming since 1995 ‘now significant’

June 11, 2011
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Global warming since 1995 ‘now significant’

Yesterday (June 11, 2011) the BBC reported on comments by Prof. Phil Jones, of the Climatic Research Unit (CRU), University of East Anglia (UEA), that the warming experienced by the planet since 1995 was statistically significant. That the trend in … Continue reading →

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Global warming since 1995 ‘now significant’

June 11, 2011
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Global warming since 1995 ‘now significant’

Yesterday (June 11, 2011) the BBC reported on comments by Prof. Phil Jones, of the Climatic Research Unit (CRU), University of East Anglia (UEA), that the warming experienced by the planet since 1995 was statistically significant....

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Reshape Package in R: Long Data format, to Wide, back to Long again

May 16, 2011
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Reshape Package in R: Long Data format, to Wide, back to Long again

In this post, I describe how to use the reshape package to modify a dataframe from a long data format, to a wide format, and then back to a long format again. It’ll be an epic journey; some of us may not survive (especially me!). Wide versus Long Data Formats I’ll begin by describing what

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