Modifications to a table
There are various ways that a table can be modified to make the information clearer or to highlight particular aspects of the data.
Alphabetic ordering of the categories is rarely best.
In tables of partitions, the value for a combined category is the sum of those for the categories that are being merged. The percentages are also added.
In tables of partitions, the values for the categories are unchanged, but the percentages should divide them by the total for the displayed categories, so they still add to 100%.
These techniques will be clearer in an example.
Road crashes by road feature
The table below shows the number of road crashes causing injury or death in New Zealand in 2005, categorised by the type of 'road feature' at the crash site.
The 'road features' were grouped into Intersections and Non-intersections in the report and are shown in different colours in the table. However the ordering of categories within the groups in the report was not particularly meaningful. Click the two checkboxes Sort by frequency to reorder the features by their frequency of accidents within each group.
Click the checkboxes Combine categories to combine the different types of intersections and non-intersections into a frequency table with two rows. This table highlights the differences between intersections and non-intersections.
Finally, expand the categories for Intersections and click Hide categories for the Non-intersections. This shows the distribution of road features for the accidents that occured at intersections. Note that hiding the non-intersection categories restricts attention to the accidents that occurred at intersections. The total therefore changes to the number of accidents at intersections and the percentages become percentages out of this new total.
Life expectancy in East Asian countries in 2005
The table of life expectancies is not a partition. However sorting the countries by life expectancy makes it far easier to understand.
Alphabetic order | Sorted by value | |||||||||
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The table is not a partition since the sum of two life expectancies is meaningless. It is therefore non-trivial to combine countries. For example, the combined life expectancy for mainland China, Hong Kong and Macao would need to take into account the different populations in these three places. (We will discuss the combination of such values in a later chapter.)