you can write a function for yourself using arrows:
#x,y: dataset as vectors
#xe,ye: errors per entry as vectors, if the errors are symmetric
arrbar<-function(x,y,xe,ye){
l<-length(x)
for (i in 1:l) {
arrows(x[i],y[i],x[i]-xe[i]/2,y[i],angle=90,length=0.05)
arrows(x[i],y[i],x[i]+xe[i]/2,y[i],angle=90,length=0.05)
arrows(x[i],y[i],x[i],y[i]-ye[i]/2,angle=90,length=0.05)
arrows(x[i],y[i],x[i],y[i]+ye[i]/2,angle=90,length=0.05)
}
}
Iasonas Lamprianou schrieb:
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.lampria...@manchester.ac.uk
______________________________________________
R-help@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.
--
_______________________________
Dipl.-Phys. Markus Schmotz
Universität Konstanz
Fachbereich Physik, Lehrstuhl Leiderer
Postfach M 676
D-78457 Konstanz
Tel.: +49 7531 88 3803, Fax: 3127
Mail: markus.schm...@uni-konstanz.de
______________________________________________
R-help@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.
