R help - Jan 2008 - error bar position setting

Hi,

I am using R on Windows XP.

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)

Here:  lat=latitte (x-axis)
          STotwoKm = Data values (y-axis)
          Var1 = Variance

Kindly help how I can plot error bar on both side of data point,

Many thanks,

Regards,
Yogesh

-- 
Yogesh K. Tiwari (Dr.rer.nat),
Scientist,
Indian Institute of Tropical Meteorology,
Homi Bhabha Road,
Pashan,
Pune-411008
INDIA

Phone: 0091-99 2273 9513 (Cell)
         : 0091-20-258 93 600 (O) (Ext.250)
Fax    : 0091-20-258 93 825

> 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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