Types of Graphs

Types of Graphs

Middle School

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Learning Objectives

• Define what line graphs, bar graphs, and circle graphs are.

• Learn when it is best to use a line, bar, or circle graph.

• Explain the important parts of a graph like the axes, title, and legend.

• Read different graphs to understand data, find trends, and make comparisons.

Key Vocabulary

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Line Graph

A graph using points and lines to show how a variable changes over a continuous sequence.

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Bar Graph

A graph using rectangular bars to compare values for different categories, showing differences at a glance.

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Circle Graph (Pie Chart)

A circular chart divided into slices to show how a whole is broken down into parts.

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Independent Variable

The variable that is changed or controlled in an experiment, usually plotted on the horizontal x-axis.

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Dependent Variable

The variable being measured whose value depends on the independent variable, plotted on the vertical y-axis.

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What Is a Line Graph?

• A line graph shows data that changes continuously over a period of time.

• The independent variable is on the x-axis and the dependent on the y-axis.

• Data points are plotted and then connected with a line to show a trend.

• Multiple data sets can be compared, and projections are shown with dashed lines.

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Multiple Choice

When is it most appropriate to use a line graph?

• To show the exact percentage of different parts of a budget.

• To show how a value changes continuously over a period of time.

• To compare the sizes of different categories that make up a whole.

• To compare the number of students in four different schools.

Types of Bar Graphs

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Bar Graphs

• Bar graphs are used to compare data across different categories.

• One variable is categorical, and the other is numerical.

• The bar's length shows the value of that category.

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Double-Bar Graphs

• They compare two different sets of data in the same categories.

• Each category will have two bars placed next to each other.

• A legend is used to show what each bar represents.

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Horizontal Bar Graphs

• These graphs are arranged horizontally instead of vertically.

• The different categories are shown on the vertical y-axis.

• An age pyramid is a special type of horizontal bar graph.

Multiple Choice

What is a primary advantage of using a double-bar graph?

• It allows for the comparison of two different data sets across the same categories.

• It is the only way to display data that changes over time.

• It shows the parts of a whole as percentages.

• It is specifically designed to show population distribution by age and sex.

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What Is a Circle Graph?

• A circle graph, or pie chart, shows data as slices of a whole circle.

• Each slice represents a category, and its size shows its percentage of the total.

• To find a slice's angle, convert its percentage into a part of 360 degrees.

• For example, a category that is 25% of the data has a 90-degree slice.

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Multiple Choice

A circle graph (pie chart) would be the best choice to display which of the following data sets?

• The height of a plant as it grows over several weeks.

• The percentages of different types of solid waste that make up a city's total.

• The number of cars sold by five different dealerships.

• The daily change in temperature over the course of a month.

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Common Misconceptions About Graphs

Misconception	Correction
Any graph type can be used for any data.	Each graph type has a specific purpose for different kinds of data.
The bigger the graph, the more accurate the data is.	The scale of a graph determines its accuracy, not its size.
A bar graph and a line graph can always be used interchangeably.	Line graphs show continuous data, while bar graphs compare separate categories.
The biggest slice on a circle graph is always the most important.	The biggest slice shows the largest amount, which may not be most important.

Multiple Choice

A scientist wants to compare the total amount of rainfall in four different cities over the past year. Which type of graph would be most effective for this comparison?

• Bar Graph

• Line Graph

• Circle Graph

• Age Structure Pyramid

Multiple Choice

How do the x-axis and y-axis on a standard line graph help in understanding the data?

• The x-axis shows the categories being compared, and the y-axis is always in percentages.

• The x-axis shows the independent variable (like time) and the y-axis shows the dependent variable (what is measured).

• The x-axis represents parts of a whole, and the y-axis represents the total.

• Both axes show different categories being compared.

Multiple Choice

A company reports its annual budget. It wants to show what percentage of the total budget is spent on salaries, research, marketing, and office supplies. Why is a circle graph the best tool for this?

• Because it allows for a direct comparison of the exact dollar amount spent in each category.

• Because it is specifically designed to illustrate the numerical proportions of different categories that make up a whole.

• Because it is the only graph that can handle four different categories of data at once.

• Because it can show how spending in each category has changed from last year to this year.

Multiple Choice

Imagine a graph showing a company's profits each month from 2020 to 2023. A solid line connects the points until the end of 2023, and a dashed line continues into 2024. What does the dashed line most likely represent?

• Projected or predicted profits for 2024 based on past performance.

• Data collected from a different, less reliable source.

• A period where profits were uncertain or not recorded.

• A comparison to a competing company's profits.

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Summary

• Line graphs show how data changes over a continuous period.

• Bar graphs are used to compare different categories of data.

• Circle graphs show data as percentages or parts of a whole.

• A clear graph needs a title, legend, and labeled axes.

Poll

On a scale of 1-4, how confident are you about choosing the right graph for a set of data?

• 1

• 2

• 3

• 4