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.