HANDLING ATTENTION POINTS◆ 181names on the horizontal axis, and so a separate key is needed
to show which number denotes which board. Where bar labels
are lengthy, always choose a horizontal bar design, like that
shown in Figure 7.3 where the health board names are easily
accommodated. Aim to use a fully informative label wherever
possible, with minimum abbreviation. This approach follows
the one-stop look-up principle discussed earlier in connection
with referencing systems.
Numerical progression. In Figure 7.2 the bar chart format cuts
out the mass of details in Table 7.1. But even so without any
pattern across the bars, the chart in Figure 7.2 is a jumble of data.
By contrast Figure 7.3 reorders the bars in a descending sequence,
showing completely clear results. The median and the two quar-
tile bars are also indicated, which would not be feasible without
a numerical progression. In all charts (except those showing
over-time patterns or categories where the sequence of values is
fixed) achieving a numerical progression is just as vital as for
tables.
Showing specific numbers. In Figure 7.2 the choice of a narrow
vertical bar layout and the use of an index of cataract operations
per 1000 population with very large data numbers makes it
impossible to show any numbers for the bars. By using a hori-
zontal bar layout, and an index showing cataract operations per
100,000 people, which generates simpler numbers, Figure 7.3
can give precise numbers for all observations. Note that these
numbers are included withinthe bar space. Avoid adding num-
bers above the bar area with vertical bar charts, or to the right of
the bars in horizontal bar charts, because in both these cases the
number will detract from the proper visual scale of the bars.
Although Figure 7.3 has an appropriate number of gridlines and
tick points for readers to be able to scale the bars, including the
numbers removes any difficulty in readers having to estimate
what the individual scores are.
Scaling and grid linesdecisions are often messed up. The two
figures here are both scaled fairly well, but the vertical scale in
Figure 7.2 could have been greater to allow more variation
amongst the small scores to be seen. With more extreme ranges
in the variation of data it is common to see charts where
the vertical scale for the bars has been set automatically by the
spreadsheet. This may highlight unusually high or low observa-
tions, but at the price of making almost invisible patterns in the