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Posts: 10
Reply with quote  #1 

I'm debating with others over the value of using decimal points, e.g., 75.8%, in labels to the left of some bullet graphs. The figures are %s and distribution is generally from low 20s to nearly 100%.

Some arguments against are 1) there is a margin of error since the figures are from survey data so the decimal point adds "false precision"; 2) it takes a user a bit longer to process the figure when first reading it because of the additional text; and 3) it's easier to recall at a later point in time w/o the decimal, e.g., 76% is more memorable than 75.8%.

I'm curious if anyone has additional arguments - for or against - or can point to any actual studies that might provide evidence related to #2 and #3 above.



Posts: 853
Reply with quote  #2 

Every one of the arguments that you've mentioned for eliminating the decimal digits is good. For monitoring purposes, how often would someone need to know the percentage at a greater level of precision? I suspect that this is seldom, so it would make sense to set it up so the user could access a precise version of the value by hovering over the less precise version that appears on the dashboard. This would make precision available in those infrequent instances when it's needed without introducing the problems that you've described.

Stephen Few

Posts: 192
Reply with quote  #3 

I usually label part of a whole information and bullet values with an integer approximation. However they are situations where higher precision is necessary.

A visual representation like bullet graph is usually displayed with its own scale. By doing that you already have a visual approximation, for given example, 75.8 is quickly decoded 75.
Tooltips suppose to give detailed information for hovered area. Using a label and a tooltip to display the same value with different levels of precision is a redundancy you do not need. In case you do so, you decode from graph 75, from label 76, from tooltip 75.8 and maybe from raw data 75.7584 (accessed by clipboard or so). If values need to be displayed, they have to have the precision required by data logic, purpose of design and media display.  A tooltip can provide more detailed information for the hovered item, but is no point in using it only for two levels of precision of the same information. If data is rendered on static media (image, PDF, paper), where tooltips are not available, then greater precision might be necessary to display the values.

If for instance you have several bullet graphs arranged within a table sorted by values, sharing the same scale, you might need to display a higher precision in order to explain the ranking of some items for which the values are visually very similar. 
I doubt that it has any relevance that certain isolated value is at 75.8% from target (for me 75% looks even more memorable than 76), but extra precision might have relevance for 4 consecutive values like 74.7, 74.9, 75.3, 75.5. 


Posts: 10
Reply with quote  #4 
Thanks for the thoughtful replies. It seems as if there will always be specific reasons why adding decimal points might make sense, but, in my view, this is a case where, in general, less is more.
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