I think the overriding factor is that cognitively our visual perception tells us the bars are showing length, because the bars start and end somewhere. Even “knowing” that it’s the top endpoints of the bars that encodes the values does not overcome what we see, which are the top and bottom endpoints of the bars, and the bars themselves between these endpoints.

Firstly, great site, please keep up the good work.
I really am very grateful for the time you put into passing on your insights.

I think this distinction between values encoded by their position, and values encoded by their length, is interesting.

(coming at this from a largely lay-person perspective)
While I appreciate that the presence of a ‘bar’ below the ‘top line’ of a bar in a bar chart could have assumed, or subconcious/implied(?) meaning, if we can assume that we are not using a stacked bar chart, and that all the points start on the same level, are we not effectivley looking at the ‘top line’ and its relative potision to other ‘top lines’? A kind of disconnected line chart. (ie. points encoded by their position)

Now, i’ll admit that if we were to lop off the bottom of a bar chart, and start some way up the axis, you would lose the ability to quickly gauge the changes between years (in this case), as they relate to each years totals (ie. did that loss of 3 represent a reduction of ~5%, or ~50%).
but do you not suffer the same loss in a line chart?

does this come down to one better method (bar) for comparing any year to any other, and one better method (line) for the trend over many years?
or is there some other aspect that is lost when you start a bar chart from half way, that isn’t such a factor with line charts.

Btw, I am not sure a line-graph does not produce the same misinterpretation. In several circles, line graphs, bar graphs and area plots are used interchangeably. People don’t necessarily pay attention to the fact that line graphs should be used mainly to depict time-series.

One possible Min could be the minimum tax rate in industrialized countries. It could be the min-rate in top 30 industrialized nations or the top 30 countries in terms of per capita GDP. This would set an effective baseline at the bottom end. How low would the tax rate need to go to match the lowest number available? The lowest based on OECD data from 2005 is about 18% in S Korea. New Zealand is about 20% as well.

And the max could then be the maximum rate of industrialized countries. The number that I get from the OECD survey is 45% in Germany. Now I am not sure whether this is a net tax rate (pretty sure it is not, seems too high) or a marginal tax rate on the highest incomes (45% seems too low).

So a range between about 15% to 45% with the appropriate reasoning provided for Mins and Maxes seems to be the right answer in this case.

Kain’s chart is clearly meant to deceive (glad he chimed in). Mike mentioned the problem with the distortion here as well. Any trend can be flat-lined by exaggerating the value axis beyond reasonable limits.

Unless that’s your objective, of course.

You could use my routine to Label Last Point for Excel 2007. Also, the way 2007 antialiases the magenta background makes it not completely disappear when it’s assigned as a transparent color.