Analyzing Bar and Pie Graphs

General education students in the United States lag behind their peers worldwide in the ability to read and analyze graphs and charts.  In my experience, for students with visual impairment, this deficit is even more pronounced.  This skill is very important in comprehending scientific data as it allows the reader to process data quickly and compare it.  Research has shown that we understand data better when presented as graphics.
 
This blog will give a simple description of bar graphs and pie graphs and instruction on teaching students with visual impairment how to read these graphs.   This blog will provide appropriate instruction for both blind students and low vision students.    It will be followed by a blog next month providing instruction on teaching students with visual impairment to make bar graphs and pie graphs.  Please see the following blog for more general information on reading various tactile graphics. http://www.perkinselearning.org/accessible-science/tips-reading-tactile-graphics-science-focus-state-assessment  
 
Students need to understand what type of data to expect  in a bar graph versus a pie graph.    Bar graphs allow us to compare how something changes over time or to compare groups of data whereas pie graphs show the relationship of parts to the whole.  Describe this to students before beginning instruction.  It is also important to understand the title and labels of the graph.
 

Bar Graphs (aka Bar Charts)

I will refer to the bar graph below as a reference.  However, it is not necessary to use this bar graph with your students.  I would recommend beginning with a fairly simple bar graph, though, which does not indicate negative numbers and has labels on each axis.  Ideally, either bar graphs from content covered in science class or a bar graph on a topic of interest can be utilized. Students should be introduced to numerous bar graphs over a period of several weeks or months in order to master this skill.
This graph is described in the text.
 
Step 1:  Read the title -  in this case "Annual Growth of Subscriber base (in millions)".  Ask the student to think about what type of information this graph will provide and discuss.  Start with a simple graph. 
 
Step 2:  Reading a key.  If there is a key, remind the student that the information on the key should be found after brief initial exploration of the bar graph. A key would be necessary on a bar graph if there is not enough room for the labels on the graph.   Discuss the key if appropriate.  A braille student will need to have a point on the graph (a point of origin) to return to each time he/she goes back and forth from the graph to the key.
 
Step 3:  Read the Y-axis (The vertical axis)  This axis will typically have a range of values which will provide a measure of th frequencey of data.  The two axes however, may be switched.  I would recommend beginning instruction with a bar graph set up in this more typical manner, though.  Have the student read the label and the values on the Y axis.  In this case the label indicates "Size of subscriber base (in milions)" and the range of values is from 0 to 700 (million).  
 
Step 4:  Read the X-axis (The horizontal axis).  This axis will typically have information about what type of data is shown.  This may be a comparison of different items or change over time.  On the graph below this axis indicates "At the end of financial year".  On this graph we understand that the information from each bar relates to the subscriber size (per the Y axis) at the end of the given financial year (per the X axis) 
 
Step 5:  Discuss the meaning of the data given in the bar graph.  In this case, questions like, "What has occured over time to the number of subscribers?" or " About how many times more subscribers were there in 2009 than in 2002?"  The questions discussed will relate to the graph and should be at the appropriate level for the student.
 
 

Pie Graphs (aka pie charts)

Pie charts compare pieces of data to the whole.  Explain to the student that the size of the sector (piece of the pie) which refers to each item is comparable to the amount of that labeled data.  Please refer to the following pie graph
This pie graph is described in the text.
 
Step 1:  As with a bar graph, the first thing students should read is the title.  In this case, "Survey on Why People Travel"  Discuss what this pie graph will communicate. 
 
Step 2:  Reading a key.  If there is a key, remind the student that the information on the key should be found after brief initial exploration of the pie graph. In this case, the pie graph would likely have a key if it were produced as a tactile graphic as there wouldn't be room in the pie graph for the labels.  Discuss the key if appropriate.
 
Step 3: Read labels. The labels on this graph include the various reasons that people might travel.  Have students compare the relative frequencies of the categories on the sectors(pieces) of the pie graph.  Have the student place these in order from greatest to least.  Other related questions can be composed depending on the student's math ability. 
 
teaching graphs collage
 
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