4. Read and translate the text:

The main reasons why you should be using tables and graphs to display your data are:

• (in the early stages of statistical analysis) to explore and to understand the data;

• (when preparing a report or a presentation) to make your points clearly.

Tables and graphs will enable you to describe, compare and contrast variables, show relationships between variables, and present in a ‘picture’ what would take a great many words to describe. In general, categorical and numerical data use different tables and graphs.

Tables present information in rows and columns, and should be used when you want to summarise information so that specific values can be grasped quickly and easily. Besides ‘normal’ tables that don’t require any calculations other than percentages, there are others which produce the results of statistical tests in a comprehensible and concise way.

A frequency table or frequency distribution summarises the number of cases in each category for a variable. This table is very helpful when you are starting out to examine your data. It gives the total number (and, if calculated, the percentage) of times each category or value occurs (the frequency with which it occurs). This is often represented by statisticians by the lower-case letter f, whilst the lower-case letter x is used to represent all the individual data values of a variable.

Cross-tabulations or cross-classification tables are used when you need to present a table that summarises more than one variable at the same time. In these two-way tables, the categories of one of the variables form the rows and the categories of the other variable form the columns. When you interpret your cross-tabulation, remember that while the one variable doesn’t cause the other, the table does show the relationship between the two variables.

Before this type of table could be included in a report or presentation, it would be important to use more easily understandable names for each of the variables, replace the codes for each variable with their labels, add a title and state the source of the data the table contains . As a rule of thumb, your table should be clear enough to allow it to be understood without having to read any of your text!

There are a wide range of graphs available. However, only some of these are suitable for presenting categorical data. Those most frequently used are summarised in Table 11.1 along with when to use them. Those shaded in Table 11.1 are the ones you are most likely to use. You will probably have little use for those graphs not shaded.

Table 11.1 Graphs for presenting categorical data and when to use them

Graph	Use when you want to present data to
Bar chart	show frequency of occurrence and emphasise highest and lowest categories for one variable (frequencies are normally displayed vertically and categories horizontally) show the trend for one variable over time (frequencies are normally displayed vertically and discrete time periods horizontally)
Pie chart	emphasise proportions in each category for one variable
Multiple bar chart	compare frequency of occurrence for two or more variables, emphasising highest and lowest categories (frequencies are normally displayed vertically and categories horizontally) compare the trends for two or more variables over time (frequencies are normally displayed vertically and discrete time periods horizontally)
Pictogram	emphasise highest and lowest categories for one variable
Stacked bar chart	compare frequency of occurrence for two or more variables, emphasising the variables’ totals (frequencies are normally displayed vertically and categories horizontally)
Percentage component bar chart	compare proportions in each variable category for two or more variables (proportions are normally displayed vertically and categories horizontally)
Comparative pie chart	compare proportions in each variable category for two or more variables
Comparative proportional pie chart	compare proportions in each variable category and relative totals for two or more variables