Comparing Two Distributions

August 29, 2011 | 0 Comments

Here I compare two distributions, flowering duration of indigenous and allochtonous plant species. The hypothesis is that alien compared to indigenous plant species exhibit longer flowering periods. Read more » [Read more...]

Example 8.34: lack of robustness of t test with small n

April 12, 2011 | 0 Comments

Tim Hesterberg has effectively argued for a larger role for resampling based inference in introductory statistics courses (and statistical practice more generally). While the Central Limit Theorem is a glorious result, and the Student t-test remarkabl...
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Manual variable selection using the dropterm function

May 12, 2010 | 0 Comments

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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Design of Experiments – Power Calculations

November 18, 2009 | 0 Comments

Prior to conducting an experiment researchers will often undertake power calculations to determine the sample size required in their work to detect a meaningful scientific effect with sufficient power. In R there are functions to calculate either a minimum sample size for a specific power for a test or the ... [Read more...]

Paired Student’s t-test

July 26, 2009 | 0 Comments

Comparison of the means of two sets of paired samples, taken from two populations with unknown variance.A school athletics has taken a new instructor, and want to test the effectiveness of the new type of training proposed by comparing the average time...
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Two sample Student’s t-test #2

July 25, 2009 | 0 Comments

Comparison of the averages of two independent groups, extracted from two populations at variance unknown; sample variances are not homogeneous.We want to compare the heights in inches of two groups of individuals. Here the measurements:A: 175, 168, 168...
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Two sample Student’s t-test #1

July 24, 2009 | 0 Comments

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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