Help in understanding the graphs in technical papers

[sk381]

When one sees graphs that are published in research papers and journal
articles, all data points have little rods with bars on them
protruding from them on either side..
What are these for and how does one interpret them?

Thanks

[ZapperZ]

Originally posted by sk381
When one sees graphs that are published in research papers and journal
articles, all data points have little rods with bars on them
protruding from them on either side..
What are these for and how does one interpret them?

Thanks

It would help if you cite the papers you see these from. But assuming that I think I know what you are refering to, these "bars" are error bars. They are the "plus-minus" values in the uncertainty of the data points.

Zz.

[sk381]

Is there any link that you can suggest where I can learn how to make these using excel etc.. and also the theory behind them.. Also since the graphs themselves are so small, are these bars conveying any real information except giving a qualitative feel foe the amount or error.. sort of like the the distance bar in a map..

[ZapperZ]

Originally posted by sk381
Is there any link that you can suggest where I can learn how to make these using excel etc.. and also the theory behind them.. Also since the graphs themselves are so small, are these bars conveying any real information except giving a qualitative feel foe the amount or error.. sort of like the the distance bar in a map..

The graphs in most physics papers that are published are mainly to convey some messages. They are not meant for one to actually get an exact quantity directly from. Typically, if one is interested in the actual data, one contacts the author/s directly. That is why they are small and only try to convey a general idea only. This is especially true in journals such as Phys. Rev. Lett. that has a page limit of only 4 typeset pages - most authors try to cram as much as they can in those pages resulting in graphs that are sometime small.

I have no idea how to do that using Excel, nor would I recommend using it to make scientific graphs (it isn't meant to do that). If you're in school, there are many graphing software that have special student/educational discounts. Try looking at Kaleidagraph, PsiPlot, Origin (which is what I use), SigmaPlot, etc. However, I think I just made the assumption here that you're in a US educational institution, which may nor may not apply to you.

Zz.

[Integral]

Excel is designed for business applications, it STINKS for scientific style work. One can nearly create error bars using stock hi lo charting, it is hard and does not work well. Generally you will not see error bars on Excel charts. I make lots of what excel calls scatter charts but even that is weak for real data, because you need to have the same x values for all data series, frequently, this is not how real data is recorded.