t-test

Comparing Two Distributions

August 29, 2011 | Kay Cichini

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...]

One-way ANOVAs in R – including post-hocs/t-tests and graphs

May 11, 2011 | Hayward Godwin

In this post, I go over the basics of running an ANOVA using R. The dataset I’ll be examining comes from this website, and I’ve discussed it previously (starting here and then here). I’ve not seen many examples where someone runs through the … Continue reading → [Read more...]

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

April 12, 2011 | Nick Horton

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 | 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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Design of Experiments – Power Calculations

November 18, 2009 | Ralph

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 | Todos Logos

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 | Todos Logos

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 | 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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