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Adding Standard Deviation to Scatter Data


EEasley
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Hi-

 

I am adding scatter data to a GTPlot reaction path that I created in REACT. I would like to include error bars on the scatter data, but I am not sure how to go about adding the standard deviations in the spreadsheet. I have already calculated the standard deviation of each analyte in Excel for major cations and anions, and then I am using the reported standard deviation by GeoTech, who rents the multimeter I used to measure field pH and temperature. Basically, I would like to simply add that the pH has a standard deviation of +/- 0.2 pH units and that temp has a standard deviation of 0.15 degrees C. Is there a simple way to just add in the standard deviation, or do I have to enter the standards and measured values in the GSS spreadsheet (as described in the user guide). My main concern is that I am only using reported standard deviation values from the equipment provider for pH and temperature, as I didn't run any calibrations myself (but now I am thinking I should have!). Please let me know if you have any suggestions! Thanks!

 

Elisabeth Easley

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Hi Elisabeth,

 

All you need to do to set errors bars is enter a triplet of values separated by vertical bars in each cell of your GSS spreadsheet. For pH, put in 6.3|6.5|6.7, for example, to create error bars of standard deviation 0.2 about a measured pH value of 6.5. Unfortunately you cannot just enter a standard deviation value once and have it apply for all your datapoints. This may be a bit tedious, but that is how the program is set up right now.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

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Hi Elisabeth,

 

All you need to do to set errors bars is enter a triplet of values separated by vertical bars in each cell of your GSS spreadsheet. For pH, put in 6.3|6.5|6.7, for example, to create error bars of standard deviation 0.2 about a measured pH value of 6.5. Unfortunately you cannot just enter a standard deviation value once and have it apply for all your datapoints. This may be a bit tedious, but that is how the program is set up right now.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

 

Hi Brian-

 

Thanks. I was able to calculate the standard deviation as you described above. I'm not having any success in getting the error bars on an XY plot though...is there a setting that I am missing?? I made sure that the sample points were small enough so that they wouldn't overlap the margin of error, but the actual error bars don't show up. I tried plotting an XY of pH vs Temp in the original GSS spreadsheet, and also as scatter data on a reaction path GTPlot of pH vs temp, but no error bars. Thanks for your help!

 

Elisabeth

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Hi Elisabeth,

 

Your problem was that you didn't put the range of values for each sample in a single cell. I've made you a GSS spreadsheet that will show you how to enter in your data. You'll want a row for each analyte (pH and Temperature) and columns for each sample. You can enter in three values in a single cell, separated by a vertical bar (|), to represent the data point itself and the ends of the error bar. If you enter in two values separated by a double bar (||) you will get just the error bar. Of course, entering a single value per cell will give you a standard data point.

 

Hope this helps,

 

Brian

Nov pH T with ST DEV.gss

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Hi Brian-

 

Got it. Yes, it is quite tedious to plot the errors in this manner for large datasets! Do you forsee any addition to the program that incorporates a more simple function for plotting errors? When you are using geochemical data to verify or support reaction path models, it is nice to have the error bars, however it is a little too time consuming to plot them in this way for large datasets that include 20+ analytes that each have an associated error! Thanks very much for your help, I really really appreciate it!

 

Best,

Elisabeth

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