Table pitfall

Happy New Year to you all!  I'm now back from holiday.

At work today, I came across this data table (shown right is a small extract from the very large data table, with labels changed to protect the innocent).  I was scanning through the numbers, looking for differences between type A and type B samples.

If your eyes work like mine, you may pick out the "West" region comparison, mainly because of the jump in the leading digit.  But then I circled back, because the right side of my brain wanted both columns to add up to 100% (less rounding) and something has to compensate for the 15-21 jump.  After a moment's search, after finding the 35-30 flip in the "South" region, I let go a sigh of relief.

Even though the above differences were about the same (5 or 6 percentage points), my eyes caught the change in leading digits and stuck to it.  This problem is especially acute when scanning quickly through reams of data tables.

So data analysts beware!  This includes those who scan financial statements, financial data, computer-generated logs, statistical software output (e.g. SAS), market research data, etc. for a living.  We are easily fooled.

Not convinced?  Let your eyes decide which difference is larger: