Displaying meaningful data

It is important to think carefully about which values to present in tables. In some situations, the most obvious data are not the easiest to interpret, but a simple ratio or difference of values is much more easily understood and meaningful. A few examples will illustrate.

Percentages and proportions

In simple frequency tables, it is often easier to understand the proportions (or percentages) in the different categories than the raw counts.

This is even more important when comparing the distribution of a categorical variable in several groups, especially if the total number of individuals differs between the groups.

It is much easier to compare proportions or percentages between groups than to compare raw frequencies.


Tourists in Hawaii

In 2005, a survey was conducted of tourists arriving in Hawaii. The following table is based on the results of that survey and shows the total number of tourists (in thousands) who arrived in Hawaii in 2005 from the most important originating regions, and categorised by their 'lifestage'.

  US West US East Japan Canada Europe
Wedding/honeymoon 103.1 110.0 192.7 8.0 131.5
Family (with children) 667.1 297.1 485.6 44.5 94.4
Young (18-34) 403.3 243.1 229.1 38.8 210.1
Middle aged (35-54) 955.2 634.7 308.0 75.1 374.2
Seniors (55+) 903.7 643.5 303.5 82.3 314.6
Total 3,032.5 1,929.3 1,517.4 248.6 1,123.7

Each column of this table is a frequency table for tourists arriving from one region. However it is difficult to make meaningful comparisons between the regions since their totals are so different.

The following table shows each column as percentages.

  US West US East Japan Canada Europe
Wedding/honeymoon 3.4 5.7 12.7 3.2 11.7
Family (with children) 22.0 15.4 32.0 17.9 8.4
Young (18-34) 13.3 12.6 15.1 15.6 18.7
Middle aged (35-54) 31.5 32.9 20.3 30.2 33.3
Seniors (55+) 29.8 33.3 20.0 33.1 28.0
Total 100.0 100.0 100.0 100.0 100.0

In this form, it is much easier to understand the differences between the types of tourist from the different regions. In particular, it is clearer that:

A bigger proportion of tourists from Japan are Wedding/honeymoon and Family than from the other regions. Also, more tourists from Europe are Wedding/honeymoon but very few are Family.


Ratios

In some situations, the rows of a table correspond to items of different 'size'. Dividing values by a measure of size can then make it easier to compare rows. For example,


TB cases in SADC countries

The next table shows the numbers reported cases of TB in the countries of the Southern African Development Community (SADC) in 2005. (Figures from Mauritius were unavailable.)

The largest numbers are associated with the countries with the biggest population, so the table mainly tells you about the sizes of the countries.

Click Show Cases per 1000 to add a column showing the populations of the countries and a final column containing the ratio of TB cases to the population size. This last column shows the TB cases per 1000 of population, so the values in different countries can be more meaningfully compared.

Note that the table only describes reported TB cases, so some of the smaller rates are caused by under-reporting, not just better health.

Finally, use the '-' button to reduce the digits displayed for the TB rates. Two significant digits would be sufficient in most reports.

Wine production in New Zealand

The table below gives the wine production (in tonnes) in New Zealand from 1986 to 2001.

Although these values show considerable variation in wine production between 1986 and 2001, with a slightly increasing trend, there was also a great increase in the area of vineyards in this period. Click Show Yield to see the area of vinyards (hectares) and the yield (tonnes per hectare).

Use the '-' button to reduce the number of decimal digits in the column of yields.

The yield from vinyards in New Zealand increased until about 1990, but has dropped sharply in more recent years.

Various factors might explain the drop in wine yields — for example, use of land that is less well suited to vines or a move to higher-quality varieties.