1.2 - Displaying quantitative data with graphs (Histograms)
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Transcript of 1.2 - Displaying quantitative data with graphs (Histograms)
1.2 - Displaying quantitative data with
graphs(Histograms)
HistogramsThe most common graph of quantitative data.
(not the most convenient)
Classes: the intervals along the bottom axis. These need to be of equal width
Frequency: the count of individuals of a class occurring
Relative frequency: the percent of the individuals in a class
(this is more useful, especially when you are comparing two sets of data with an unequal total
of individuals)
Door Side
The following table represents the battings averages for the 25 Cincinnati Reds who
have an at bat this time in the 2013 season.
0.36 0.342 0.29 0.275 0.271
0.268 0.262 0.26 0.25 0.247
0.245 0.24 0.235 0.221 0.218
0.163 0.16 0.15 0.13 0.114
0.111 0.109 0.056 0.000 0.000
Wall Side
The following table represents the battings averages for the 29 Cincinnati Reds who
have an at bat this time in the 2014 season.
0.289 0.284 0.279 0.272 0.271
0.271 0.269 0.255 0.239 0.238
0.224 0.224 0.221 0.212 0.153
0.151 0.146 0.145 0.143 0.139
0.114 0.100 0.080 0.056 0.000
0.000 0.000 0.000 0.000
Steps for constructing a histogram
1st - divide the range of data into class of equal width.
2nd - find the count and percent of individuals in each class.
3rd - label and scale your axes
4th - draw your histogram
1st stepWhat is the range of our data?
What would be a good class size to choose?
What are the classes?
2nd StepFill in a frequency table and a relative frequency
table.Frequency
TableClass Count
Relative Frequency Table
Class Percent
3rd step
Batting Average
Rela
tive F
requ
en
cy
Batting Average
Rela
tive F
requ
en
cy
2013 2014
Describe the data of the batting average for YOUR year only!
Don’t forget your “SOCS!”
The data appears to be _______
with a peak of _____ .
The _____ appear to be any outliers.
The center of the data
occurs around ______
The histogram shows that the batting
ranged from
__________
Now let’s COMPARE the batting averages from
2013 and 2014
How does class size effect the shape of the
histogram?
www.whfreeman.com/tps4e
Last Pieces of advice about histograms
1. Don’t confuse histograms and bar graphsHistograms are for quantitative dataBar graphs are for categorical data
4. Just because a graph looks nice, doesn’t mean it’s necessarily a
meaningful display of data. (Excel is a terrible tool to use for
statistical graphs)
3. Use percents instead of counts when comparing distributions with different numbers of
observations.
2. Don’t use the counts or percents as the data. Use the data to find the counts and percents for your
graph.