GRAPHS

PREPARED BY: ENAWOID

aims:

Interpret and analyze graphs to determine what information is given.

Complete exercises by applying data and graph concepts.

Self-assess knowledge and skills acquired from this unit.

Develop problem-solving skills.

DEFINITION:

A graph is a visual representation of a relationship between, but not restricted to, two variables. A graph generally takes the form of a one- or two-dimensional figure such as a scatterplot. Although, there are three-dimensional graphs available, they are usually considered too complex to understand easily.

A graph commonly consists of two axes called the x-axis (horizontal) and y-axis (vertical). Each axis corresponds to one variable. The axes are labelled with different names, such as Price and Quantity.

The place where the two axes intersect is called the origin. The origin is also identified as the point (0,0).

A GOOD GRAPH

accurately shows the facts grabs the reader's attention complements or demonstrates arguments

presented in the text has a title and labels is simple and uncluttered shows data without altering the message of the

data clearly shows any trends or differences in the

data is visually accurate (i.e., if one chart value is 15

and another 30, then 30 should appear to be twice the size of 15).

Why use graphs when presenting data?

are quick and direct highlight the most important facts facilitate understanding of the data can convince readers can be easily remembered

Graphs: four guidelines

1. Define your target audience.

Ask yourself the following questions to help you understand more about your audience and what their needs are: 

Who is your target audience? What do they know about the issue? What do they expect to see? What do they want to know? What will they do with the information?

2. Determine the message(s) to be transmitted.

Ask yourself the following questions to figure out what your message is and why it is important:

What do the data show? Is there more than one main message? What aspect of the message(s) should be

highlighted?

3. Determine the nature of the message.

4. Experiment with different types of graphs and select the most appropriate.

pie chart (description of components) horizontal bar graph (comparison of items and

relationships, time series) vertical bar graph (comparison of items and

relationships, time series, frequency distribution)

line graph (time series and frequency distribution)

scatter plot (analysis of relationships)

TYPES OF GRAPHS

1. bar graph may be either horizontal or vertical. The important point to note about bar graphs is their bar length or height—the greater their length or height, the greater their value.

Bar graphs are one of the many techniques used to present data in a visual form so that the reader may readily recognize patterns or trends.

3. Pictograph - uses picture symbols to convey the meaning of statistical information. Pictographs should be used carefully because the graphs may, either accidentally or deliberately, misrepresent the data. This is why a graph should be visually accurate.

4. Pie chart is a way of summarizing a set of categorical data or displaying the different values of a given variable (e.g., percentage distribution). This type of chart is a circle divided into a series of segments. Each segment represents a particular category. The area of each segment is the same proportion of a circle as the category is of the total data set.

5. Line graph is a visual comparison of how two variables—shown on the x- and y-axes—are related or vary with each other. It shows related information by drawing a continuous line between all the points on a grid.

Line graphs are more popular than all other graphs combined because their visual characteristics reveal data trends clearly and these graphs are easy to create. Line graphs, especially useful in the fields of statistics and science, are one of the most common tools used to present data.

Pictograph uses an icon to represent a quantity of data values in order to decrease the size of the graph. A key must be used to explain the icon.

Advantages Easy to read Visually appealing Handles large data sets easily using keyed icons

Disadvantages Hard to quantify partial icons Icons must be of consistent size Best for only 2-6 categories Very simplistic

Pie chart displays data as a percentage of the whole. Each pie section should have a label and percentage. A total data number should be included.

Advantages Visually appealing Shows percent of total for each category

Disadvantages No exact numerical data Hard to compare 2 data sets "Other" category can be a problem Total unknown unless specified Best for 3 to 7 categories Use only with discrete data

Bar graph displays discrete data in separate columns. A double bar graph can be used to compare two data sets. Categories are considered unordered and can be rearranged alphabetically, by size, etc.

Advantages Visually strong Can easily compare two or three data sets

Disadvantages Graph categories can be reordered to emphasize certain

effects Use only with discrete data

Line graph A line graph plots continuous data as points and then joins them with a line. Multiple data sets can be graphed together, but a key must be used.

Advantages Can compare multiple continuous data sets

easily Interim data can be inferred from graph line Disadvantages Use only with continuous data