Excel Error Bars Logarithmic
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Thread Results 1 to 7 of 7 Thread: Error bars on log-transformed plots Thread Tools Show Printable Version Email this Page… Subscribe excel error bars 2013 to this Thread… Display Linear Mode Switch to Hybrid Mode Switch to Threaded Mode 04-18-200802:07 PM #1 gstuart View Profile View Forum Posts Give Away Points Posts 4 Thanks 0 Thanked 0 Times in 0 Posts http://answers.microsoft.com/en-us/msoffice/forum/msoffice_excel-mso_other/error-bars-do-not-display-correctly-on-a/91dc767c-8e62-4a42-9bca-8787278fcebd Error bars on log-transformed plots Hello - I am a genetics researcher. I have a series of data points with errors (standard errors), that I wish to plot as a graph plot: GENE, AVG FOLD CHANGE, SE Gene1, 2193.10, 1200.74 Gene2, 96.28, 9.08 Gene3, 39.02, 22.51 Gene4, 5.88, 0.82 Gene5, -0.68, 0.33 Gene6, 1.14, 0.02 Gene7, -1.46, 0.16 Gene8, -1.56, 0.50 Gene9, -1.58, 0.10 Gene10, -1.88, 0.45 Gene11, -2.04, 0.45 Gene12, -6828.82, http://www.talkstats.com/showthread.php/4304-Error-bars-on-log-transformed-plots 975.41 Positive values are up-regulated genes; negative values are down-regulated genes (re: gene expression levels). I wish to plot this as a column plot on a log scale (y-axis) with negative values below the zero baseline, positive values above, and with the errors indicated. Something like: 1000 100 10 * 1 * 0------------------- -1 * -10 * -100 -1000 but with bars instead of the asterisks - you get the idea. I can do this easily enough using MS Excel, by taking the log of the absolute value, multiplying the result by +1 or -1 (to restore the original "directionality" - i.e. up- or down-regulated). A couple of questions: (Q1) Is it "better" to use log (base 10) or ln (natural) log transformations? (Q2) How would I present the error bars - would I log (or ln) -transform the standard errors, for example, and plot these [or the absolute values of these, since the log of numbers <1 are negative; e.g. log(0.5) = -0.301)]? I tried finding the answer to these questions in Google, but I wasn't very successful. ... I would very much appreciate any comments regarding the log-transformation of data and plots of log-transformed data, particularly regarding error bars! Thank you! Sincerely, Greg :-) Reply With Quote 04-22-200803:52 PM #2 gstuart View Profile
graphs can give a concise and compact form of representation, while graphs made poorly can be misleading and very confusing. Why use logarithmical graphs? If you find yourself http://bubble.ro/Logarithmic_scale_graphs_in_Excel.html with data spread on an extremely large area, the graph will be very compact and you may miss some sharp drops in values because of this. A semi-logarithmical graph is has one of the two axes (usually the abscissa) in a logarithmical form. The logarithmical base is usually 10, but can also be “e” or any other base. Well let's suppose you have the error bars following table: X 1 2 5 10 20 50 100 200 500 1000 2000 Y 1 2 4 16 256 65536 4.29E+09 1.84E+19 3.4E+38 1.16E+77 1.3E+154 The corresponding Excel scatter chart is this: On the other hand, if you extract the logarithm of both X and Y rows you get this table: log_x 0 0.3 0.7 1 1.3 1.7 2 2.3 2.7 3 3.3 excel error bars log_y 0 0.3 0.6 1.2 2.41 4.82 9.63 19.27 38.53 77.06 154.13 And its corresponding graph: Does it make sense now? I thought so How to obtain the logarithmic graph Double click the axis that you want to be on a logarithmical scale. In the "Scale" tab, select the "Logarithmical Scale" option and click ok. Then, go to the Chart Options (in the Chart menu) and in the "Gridlines" tab check the "Minor gridlines" on the axes you want depending of the desired graph type: semi-logarithmical or logarithmical. That's it ! Hope this helps ! » Permalink Posted by: Nitro on March 18, 2006 at 14:51. » Comments Har har Very interesting. I never thought logarithmic scales would lighten up my life ;)... Posted by SunBeam on March 20, 2006 at 05:19 PM. Tip Just remember to use the normal values when you select source for the graphic, Excel does the log operation for you. Posted by Mika on March 21, 2006 at 01:18 AM. Hello, sort anoob here hello ladies and gents! I've been kind of lurking around. I love this site! thanks for having me :) Posted by