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wd

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Posts: 167
Reply with quote  #1 
Wondering if there's a best way to display change when comparing two data sets for two years - in this case when smaller is better.

1 We can subtract 2010 from 2009 and plot.  If 2010 is better the numbers are positive; if worse then negative.  Better & positive, worse & negative relate

OR

2 We can subtract 2009 from 2010 and plot.  Where 2010 is better the numbers are negative; if worse than positive.  Now down & negative, up & positive relate.

I think 1 is preferred for smaller is better but what is the best/right way?

Example attached.
Thanks

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Bill Droogendyk

bpierce

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Posts: 99
Reply with quote  #2 
Hi Bill,

I would subtract the 2009 values from the 2010 values to preserve the "lower is better paradigm." Doing it the opposite way makes larger values better, which might seem more intuitive, but if you're looking at a data set where lower is better (such as expenses), people might have already primed themselves to think that lower values are better, so calculating the deviation in a way that makes lower values appear larger could confuse them.

-Bryan
jlbriggs

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Posts: 194
Reply with quote  #3 
I think it should be clear to most people that something like material costs being expressed as a negative number is a good thing...
I don't think any visual trick is necessary to make it understood that low is good in cases like these...other than perhaps a line of text that says 'low is good'  :)



Derek_C

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Posts: 69
Reply with quote  #4 
I think just plot the two values in series and let their position indicate the year-on-year change.  If change is small compared to absolute value, then simple bar charts are not recommended, but line or dot charts are still good, as are floating bar charts (the invisible, "float", bar doesn't count as a bar that has to be displayed in its entirety).

Various floating bar chart types can add value, and go by names like waterfall, bridge, or candlestick charts.
wd

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Posts: 167
Reply with quote  #5 
Thanks all;

What's not evident (due to the font size) is that the comparison between years is for categories, i.e. comparing 2009 with 2010 for catagory A, B, C, etc.

wd

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Bill Droogendyk
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