Manual variable selection using the dropterm function

May 12, 2010 | Ralph

When fitting a multiple linear regression model to data a natural question is whether a model can be simplified by excluding variables from the model. There are automatic procedures for undertaking these tests but some people prefer to follow a more manual approach to variable selection rather than pressing a ...
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Demonstrating the Power of F Test with gWidgets

April 2, 2010 | Yihui Xie

e know the real distribution of the F statistic in linear models — it is a non-central F distribution. Under H0, we have a central F distribution. Given 1 – α, we can compute the probability of (correctly) rejecting H0. I created a simple demo to illustrate how the power changes as other parameters ... [Read more...]

Two sample Student’s t-test #1

July 24, 2009 | Todos Logos

t-Test to compare the means of two groups under the assumption that both samples are random, independent, and come from normally distributed population with unknow but equal variancesHere I will use the same data just seen in a previous post. The data ...
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