6. Graphs
Graphs show the relationship between variable quantities, typically of two variables, each measured along two axes
X-axis: Horizontal axis used for the independent variable
Y-axis: Vertical axis used for the dependent variable
A simple line graph shows only one data set.
Steps to draw a simple line graph:
Draw and label the x-axis and y-axis
Choose an appropriate scale for each axis
Plot each data value by locating the intersection between the x-axis and y-axis with a cross
Include a title for the graph
Use the following questions to help you understand the data in a line graph:
What are the largest and smallest values? In which years did they occur?
What is the average value?
What is the data range?
What is the trend or pattern? How much is the change?
A useful method in interpreting trend will be:
Overall trend - look at the start and the end point to see whether there is an increase or decrease.
Significant - Is there a period where the increase/decrease is at a faster rate or at its highest/lowest
Anomaly - is there a period where it is different from the overall trend? E.g. if overall trend is increasing, then anomaly will be decreasing
A comparative line graph is used to compare two sets of data on the same axis.
Bar graphs are rectangular bars whose lengths are proportional to value they represent.
Steps to draw a bar graph
Draw and label x-axis and y-axis
Choose appropriate scale for each axis
Ensure same spacing between the bars
Include a title
A comparative bar graph allows for the comparison of two or more data sets.
A pie chart is a circular graph which is divided into sectors.
To calculate the angle of the sector, take the percentage multiple by 3.6.
Sectors resemble pie slices and sum of all sectors is 100%
Useful for comparing the size of different sectors
When drawing a pie chart:
Arrange sectors in descending order with the biggest sector first
Label each sector or indicate it in the legend
Colour or shade the sectors
Include a title