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John S.

I agree that your version of the HIV chart looks better, but I'm not sure about the chart for retirement age. You've certainly maximized the data-to-ink ratio, but now the points just kind of hang out there, unmoored. Probably the most significant point the data make is that Japan's official retirement age does not correspond with reality (nor with the official retirement ages of other industrialized countries). However, the only visual clue to this fact is the presence of a faint gray dot.

These data are similar to the situation where there is a formula that predicts something (e.g. monthly energy use) and we want to compare the predicted and actual values. One solution I have tried -- and I'm not sure it's the right one -- is to connect the actual and predicted values with a line. The line is red if actual is less than predicted, black otherwise.

Nick Barrowman

I think that one of the reasons the bar chart is so popular is that it paints broad strokes of ink (particularly striking when color is used), giving the figure a kind of visual punch. The original figures above can be seen from halfway across a room, whereas the redrawn versions nearly disappear (admittedly I'm not wearing my glasses, but I think the point holds). However, the redrawn HIV figure could achieve a similar effect using vertical colored boxes with light horizontal lines indicating the baseline estimates.

Another reason for the popularity of bar charts may be that they connect the label with the estimate, thereby avoiding the points-hanging-out-there effect that John S noted in the redrawn retirement age figure.

Regarding the retirement age figure, John S suggests connecting pairs of values with lines. An arrow might work, since its direction could be readily interpreted. But maybe the data shown in the figure are incomplete. The official retirement age in a country is a single number, but I'm guessing the "effective retirement age" is a mean. It might be more informative to see the mean + - 1 or 2 standard deviations (or perhaps the 25th, 50th, and 75th percentiles).

Nick Barrowman

Further to my comment above, I have put an example of the alternative display I suggested on my blog. I'd be very interested in feedback!

Kaiser

Hi Nick, thanks for your thoughtful comments. The reason why I prefer lines rather than bars is that the addition of a second dimension (bar width) is somewhat distorting, drawing our attention to the area rather than height of the bars. I'll explain this point in a future post.

Responding to you and John both, I think two additional features will help the retirement age plot: (1) order the countries based on the age gap, rather than on actual retirement age -- this will do a lot to help focus the attention on the gap; (2)
connect the gray dots -- this is similar to lines in so-called interaction plots for regression.

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