Friday, March 29, 2013

Multiple histograms: Overlayed or Back to Back

We can calculate frequency with same Bins, then use then to plot histogram with grouped bar chart.  

We can overylay the histograms, with transparency. Look the following plots:

Back to back histograms 
The trick to create back to back histogram is similar to above, here we need to make the frequency negative to the series that will be plotted in the apposite side. We need to overlap the bars (perhaps in opposite direction) and optionally you can set gap width to 0. The following example are in excel 2003, tricks can be applied in similar way in another excel versions. 

Perhaps the negative number are purpose of plotting histograms, we do not want to present them as negative. We can format the axis to look like different color (such as negative appearing as red, in the following example), perhaps back to black color. Use custom format if you want negative color displayed as different color ([Blue]0;[Green]0 format will turn positive numbers to blue and negative number of green as shown in following graph or [Black]0;[Black]0 will turn the both numbers to black and remove the - sign in negative number).

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