[R] error bars

[William Revelle]

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
>
>
>
>
>
>
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