[R] error bars

[Iasonas Lamprianou]

thank you

Dr. Iasonas Lamprianou


Assistant Professor (Educational Research and Evaluation)
Department of Education Sciences
European University-Cyprus
P.O. Box 22006
1516 Nicosia
Cyprus 
Tel.: +357-22-713178
Fax: +357-22-590539


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


--- On Tue, 30/3/10, William Revelle <lists at revelle.net> wrote:

> From: William Revelle <lists at revelle.net>
> Subject: Re: [R] error bars
> To: "Iasonas Lamprianou" <lamprianou at yahoo.com>, r-help at r-project.org
> Date: Tuesday, 30 March, 2010, 13:56
> Iasonas,
> 
> In response to PS.1
> try error.bars in the psych package.
> 
> Bill
> 
> 
> 
> At 1:04 AM -0700 3/30/10, Iasonas Lamprianou wrote:
> >Dear friends,
> >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 
> >http://scienceblogs.com/cognitivedaily/2007/03/ill_bet_you_dont_understand_er.php
> >
> >jason
> >
> >Dr. Iasonas Lamprianou
> >
> >
> >Assistant Professor (Educational Research and
> Evaluation)
> >Department of Education Sciences
> >European University-Cyprus
> >P.O. Box 22006
> >1516 Nicosia
> >Cyprus
> >Tel.: +357-22-713178
> >Fax: +357-22-590539
> >
> >
> >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
> >https://stat.ethz.ch/mailman/listinfo/r-help
> >PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> >and provide commented, minimal, self-contained,
> reproducible code.
> 
> 
> -- 
> William Revelle       
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