Bar Graphs and Histograms (7-3)

Bar Graphs and Histograms

Vocabulary

Bar Graph- displays a set of data graphically, Bars of different lengths are drawn to show the size
                  (frequency) of each group of data in the set.

Double-Bar-Graph- each data group (set) has two or more bars of different colors, each of which
                                representing a subgroup of that data.

Histogram- a bar graph that shows frequency of the data within equal intervals. There is no space
                   between the bars in a histogram.

Examples 


What is the difference between a bar graph and a histogram?


There are two differences, one is in the type of data that is presented and the other in the way they are drawn.
In bar graphs are usually used to display "categorical data", that is data that fits into categories. For example suppose that I offered to buy donuts for six people and three said they wanted chocolate covered, 2 said plain and one said with icing sugar. I would present this in a bar graph as:


Histograms on the other hand are usually used to present continuous data", that is data that represents measured quantity where, at least in theory, the numbers can take on any value in a certain range. A good example is weight. If you measure the weights of a group of adults you might get and numbers between say 90 pounds and 240 pounds. We usually report our weights as pounds or to the nearest half pound but we might do so to the nearest tenth of a pound or however acurate the scale is. The data would then be collected into categories to present a histogram. For example:


might be a histogram for heights (with the appropriate scale on the vertical axis). Here the data has been collected into categories of width 30 pounds. The difference in the way that bar graphs and histograms are drawn is that the bars in bar graphs are usually separated where in histograms the bars are adjacent to each other. This is not always true however. Sometimes you see bar graphs with no spaces between the bars but histograms are never drawn with spaces between the bars.
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Video Help

https://www.youtube.com/watch?v=Vpd1SYWwYV0

https://www.youtube.com/watch?v=h3QoquxnfZk

https://www.youtube.com/watch?v=iYIuqvuGvAw

BAR GRAPHS	HISTOGRAMS
graph title and labeled axes	graph title and labeled axes
Bars do not touch.	Bars do touch.
Vertical scale is frequency.	Vertical scale is frequency.
categorical data	numerical data