[R] error bars
lists at revelle.net
Tue Mar 30 14:56:31 CEST 2010
In response to PS.1
try error.bars in the psych package.
At 1:04 AM -0700 3/30/10, Iasonas Lamprianou wrote:
>I have a statistical question. Sometimes, if I compare boys to girls
>on a specific variable, the error bars (confidence interval of
>means) seem to overlap slightly. Still, when I run a t-test, I find
>statistically significant differences. The rule is clear: if the
>confidence intervals do not overlap, then there is statistically
>significant difference. But if they overlap slightly, we have to use
>a t-test to know for sure if the the two means differ significantly.
>The point is: is there a rule of thumb to say, for example, "if the
>overlap is less than 20% of the length of the standard error, then a
>t-test would give significant results?"
>thank you for your time
>P.S.1 is there an easy way to plot error bars in R?
>P.S.2 an interesting discussion about this - highly recommended to
>read it - can be found at
>Dr. Iasonas Lamprianou
>Assistant Professor (Educational Research and Evaluation)
>Department of Education Sciences
>P.O. Box 22006
>Honorary Research Fellow
>Department of Education
>The University of Manchester
>Oxford Road, Manchester M13 9PL, UK
>Tel. 0044 161 275 3485
>iasonas.lamprianou at manchester.ac.uk
>R-help at r-project.org mailing list
>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
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