# How do I adjust error bar tick size with ErrorListPlot?

I'm making a plot of data points from an experiment and the error bars are quite small. I would like the vertical error bars to have wider horizontal lines so that they are easier to see.

Are there any commands I can use to adjust the ErrorBar tick width? I have not been able to find anything on the documentation site and I am relatively new to Mathematica.

Here is my plot from a list of data points:

ErrorListPlot[data, Method -> {"OptimizePlotMarkers" -> False},
PlotMarkers -> "\[FilledSmallCircle]", Joined -> False,
PlotRange -> {0.00027, 0.00078}]


That is what the plot looks like. I know that the error bars are small, but I would like to make the horizontal "ticks" on the top and bottom of the error bars wider.

• Take a look at the documentation: You can customize what is drawn by your own ErrorBarFunction. Mar 21, 2015 at 17:50
• Thank you. I am not sure how to write a function that increases the line width. Do you know of any documentation that I could refer to for this matter?
– Mike
Mar 21, 2015 at 18:01
• Please see my answer for both a solution and a link to relevant documentation. :) Mar 21, 2015 at 18:58

## 1 Answer

You can use the following construct to draw the error bars yourself using any collection of geometric shapes available:

(* starting out with defining some points, errors etc. *)
pts = NestList[{#[[1]] + 1, #[[2]] + RandomReal[{0., 1.}]} &, {0,
RandomReal[]}, 19];
err = RandomReal[4, 20];
data = Table[{pts[[i, 1]], pts[[i, 2]], err[[i]]}, {i, 1, Length@pts}];

hw = 1; (* the width of the ticks *)
ErrorListPlot[data, ErrorBarFunction -> Function[{coords, errs}, {
(* the vertical line: *)
Line[{coords - {0, errs[[2, 1]]/2}, coords + {0, errs[[2, 1]]/2}}],
(* horizontal tick 1: *)
{Green,Thick,Line[{coords-{hw/2, -errs[[2, 1]]/2}, coords+{hw/2, errs[[2, 1]]/2}}]},
(* horizontal tick 2: *)
{Red,Thick,Line[{coords-{hw/2, errs[[2, 1]]/2}, coords+{hw/2, -errs[[2, 1]]/2}}]}
}]]


Example: