A graph is a diagram representing a system of connections or interrelations among two or more variables by a number of distinctive dots, lines, bars, etc.
A chart is a visual representation of data. Bar, line, pie and other types of charts are examples of charts.
Box and whisker plots (often called ‘box plots’) can be used to show the interquartile range. Figure 1 shows a box and whisker plot of student ages.
Notice that a scale is drawn underneath. Box plots can be drawn horizontally or vertically.
Frequency distribution tables can be used for nominal and numeric variables.
Twenty people were asked how many cars were registered to their households. The results were recorded as follows: 1, 2, 1, 0, 3, 4, 0, 1, 1, 1, 2, 2, 3, 2, 3, 2, 1, 4, 0, 0. This data can be presented in a frequency distribution table – see Figure 2.
Stem and leaf plots are a convenient way to organise data. Each observation value is considered to consist of two parts - a stem and a leaf.
- the stem is the first digit or digits
- the leaf is the final digit
The number of books ten students read in one year were as follows: 12, 23, 19, 6, 10, 7, 15, 25, 21, 12.
In ascending order, these are: 6, 7, 10, 12, 12, 15, 19, 21, 23, 25. Figure 3 is a stem and leaf plot of this data.
In the stem and leaf plot (fig 3):
- the stem '0' represents the class interval 0-9
- the stem '1' represents the class interval 10-19
- the stem '2' represents the class interval 20-29.
If there are a large number of observations for each stem, the stem can be split in two. For example the interval 0-9 could be split into intervals 0-4 and 5-9. The stem would then be written as 0(0) and 0(5).
A time series is a collection of observations of well-defined data items obtained through repeated measurements over time. For example, measuring the value of retail sales each month of the year would comprise a time series.
The ABS defines a trend as the long term movement in a time series without calendar related and irregular effects, and is a reflection of the underlying change in that measure. It is the result of influences such as population growth, price inflation and general economic changes.
Fig 1 Box and whisker plot
Fig 2 Frequency distribution table
|Number of cars (x)|
l l l l
|1|l l l l l
|2|l l l l
l l l
Fig 3 Stem and leaf plot
0 2 2 5 9
1 3 5