[R] error bar position setting
Richard.Cotton at hsl.gov.uk
Richard.Cotton at hsl.gov.uk
Tue Jan 22 13:44:27 CET 2008
> I am using 'arrows' funtion to plot the variance as error bar, BUT error
> bar goes only one side of the data point, I need to plot the error bar
on
> both side of the data point (plot is attached), I am using following
> commands to plot,
>
> plot(file3$lat,file3$STotwoKm,pch=21,cex=2.5,ylim=c(-0.2,2.5),
> xlim=c(-50,50),xlab=NA,ylab=NA,
> col=1, xaxs="i",yaxs="i")
>
> arrows(file3$lat, file3$var1, file3$lat,file3$STotwoKm, col=1, code=3,
> angle=90, length=0.1)
Try using the arrows function with y0 as the lower error bound, y1 as the
upper error bound and code=3, so that arrowheads are drawn at both ends of
the arrow.
You should double check the y coordinates of the arrows. If the y values
are normally distributed, then a 95% confidence interval will give lower
bounds at yvalues + qnorm(0.025)*sqrt(variance), and an upper bound at
yvalues + qnorm(0.975)*sqrt(variance).
Regards,
Richie.
Mathematical Sciences Unit
HSL
"Statistics are like a lamp-post to a drunken man - more for leaning on
than illumination."
David Brent, The Office.
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