Practical skills and field study
FOCUS QUESTION
How are tables, bar graphs, line graphs and divided circles constructed?
Tables and graphs are visual representations. They are used to organise information to show patterns and relationships.
The advantage of using a table or graph to report data is:
■ That a large quantity of information can be presented completely and accurately in a table or graph.
Tables or graphs should be constructed in such a way that the reader can easily understand the information.
TABLES
Here are some conventions to follow in constructing tables in a research paper.
1. Tables should be numbered.
■ (e.g., Table 1, Table 2, etc) This is important so that the author can refer to the table number in the text of the paper. For example, “Table 1 shows that . . . .”
2. Tables should have a title.
■ This title clearly and briefly describes the contents of the table.
3. Tables should have rows and columns that are clearly labelled.
■ This will prevent the reader from having to guess what the numbers in the table are or what they mean.
4. Tables should have the numbers in the cells of a table.
■ Numbers should be clearly identified as percentages, dollars, or other types of numbers so the readers do not have to guess what the numbers in the cells of the table mean.
A bar graph, also known as a bar chart, is a graph that uses rectangular bars to represent different values to show comparisons between categories. For example:
■ The amount of rainfall that occurred during different months of a year.
■ The average salary for different class of workers.
Bar graphs are most commonly drawn vertically, though they can also be depicted horizontally.
Please note that bar graphs are used to compare things between different groups or to track changes over time.
Bar graphs should be used to: ■ Categorise
■ Order
■ Show discrete variables
If the number of units in a discrete variable is large, it may be displayed as a continuous variable.
A. NUMBER THE Y-AXIS (THE VERTICAL ONE) – DEPENDENT VARIABLE
■ Always start numbering a bar graph at zero.
■ Only number as high as your highest value (if the highest value is 18, don’t number to 100!).
■ Line up the numbers on the lines, not in the spaces.
■ Evenly space out the numbers (number by 1s, 2s, 5s, etc) to fill up the page (don’t squeeze your graph into one corner of the paper!).
B. DRAW THE BARS ON THE X-AXIS (THE HORIZONTAL ONE) – INDEPENDENT VAR
■ Make all bars the same width. ■ Evenly space out the bars (they should not touch).
■ Label what each bar represents. ■ Colour in or shade the bars differently.
C. LABEL THE GRAPH
9. Put a label on the X-axis to tell what all of the bars represent (hobbies, months, types of plants, etc).
■ Put a label on the Y-axis to tell what the numbers represent (# of people, # of days, height of plants, etc). Make sure you include the proper unit (height of plant in inches, temperature in degrees Celsius, etc).
D. GIVE THE GRAPH A TITLE
■ The title should describe what the graph is about (The Effect of Brand of Fertilizer on How Tall the Plant Grew).
■ Put the data pairs (IV name, DV value) in the upper right-hand corner of the graph.
■ Put a box around the data pairs and label it ‘Data Pairs’.
Line graphs should be used for continuous variables. Line graphs can also be used to compare changes over the same period of time for more than one group. (The data which changes over a period of time can be displayed through a line graph.)
In line graph:
■ Points are plotted on the graph related to two variables.
■ Points are joined by the line segments.
Most line graphs only deal with positive number values, so these axes typically intersect near the bottom of the y-axis and the left end of the x-axis. The point at which the axes intersect is always (0, 0). Each axis is labelled with a data type. For example, the x-axis could be days, weeks, quarters, or years, while the y-axis shows revenue in dollars.
■ The x-axis is also called the independent axis because its values do not depend on anything. For example, time is always placed on the x-axis since it continues to move forward regardless of anything else.
■ The y-axis is also called the dependent axis because its values depend on those of the x-axis: at this time, the company had this much money.
HOW TO CONSTRUCT A LINE GRAPH?
1. Find the range in values.
There are two sets of values. What units are used? What is the greatest value and the least value for the first set? What is the greatest value and the least value for the second set?
2. DETERMINE A SCALE
Start with the horizontal scale. If you are using graph paper, let 1 unit on the graph paper equal 1 unit of the values you are graphing. Determine whether the greatest value will fit on the graph. If it doesn’t, then change the scale and try again. Now repeat this process for the vertical scale.
3. LABEL THE GRAPH
Mark each unit across the horizontal scale and along the vertical scale. Label the marks by the units they represent.
4. PLOT THE POINTS AND CONNECT THEM
Plot a point for each pair of values. Which item of a pair is indicated by the horizontal scale and by the vertical scale? How many points will you plot? Connect the points with straight lines from left to right.
5. GIVE THE GRAPH A TITLE
Pie graphs (sometimes called pie or circle charts) are used:
■ To show the parts that make up a whole.
■ For comparing the size of relative parts.
Pie charts are best to use when you are trying to compare parts of a whole. They do not show changes over time. To draw a pie chart, we need to represent each part of the data as a proportion of 360, because there are 360 degrees in a circle. Before you draw the pie chart, remember to check that the angles which you have calculated add up to 360 degrees.
In the next lesson, we will look how to construct climate graphs and dot maps. We will also look at measures of central tendency: mean, median and mode.