The relationship between flight delays and customer

HANDLING ATTENTION POINTS names 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 lookup 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 overtime 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 horizontal bar layout, and an index showing cataract operations per people, which generates simpler numbers, Figure can give precise numbers for all observations. Note that these numbers are included within the bar space. Avoid adding numbers 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 lines decisions 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 observations, but at the price of making almost invisible patterns in the

1 8 AUTHORING AP H D
variations of most of the other scores. Try to use zero wherever feasible as the scale starting-point fora graph. Where you must choose a starting-point different from zero (called suppressing the zero, always indicate that you have done so, usually by inserting a zigzag bit at the lower end of the relevant scale line,
or including a note to remind readers. It is also common to see far too many gridlines and tick points being used on the vertical or horizontal scales, which can make charts look cluttered.
Two- or three-dimensional charts.
Figure 7.2 is made more complex to read by the choice of a three-dimensional format,
with a depth axis added by the spreadsheet. Many PhD students choose D charts, thinking that they will look more sophisticated but not focusing clearly on what extra value- added the extra dimension gives (which is very little with only one data series, as here. Where several data series are shown together, adding the third dimension is potentially more useful 2
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Trtmnt rates/pop
Key:
The health boards areas follows 1 Argyll & Clyde 2 Ayrshire & Arran; 3 Border
4 Dumfries & Galloway 5 Fife 6 Forth Valley 7 Grampian; 8 Greater Glasgow 9 Highland Lanarkshire; 11 Lothian; 12 Orkney 13 Shetland 14 Tayside; 15 Western Isles.

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