Histograms

1
Histograms Adding a Second Variablein SPSS

• Chapter 4
• SPSS Holcomb
• EDLD 6333 F07

2
Histograms Adding 2nd Variable in SPSS

• Learning Objectives
• Learn what a histogram is used for
• Understand difference b/w histograms bar charts
• Learn to add a second variable in SPSS
• Create a histogram using SPSS
• Understand usefulness
• of a Normal Curve

3
Histograms Adding 2nd Variable in SPSS

• Learning Objectives cont.
• Understand use of a Normal Curve
• Place a normal curve on a histogram
• Understand difference between terms for a graph
  a figure
• Learn to format an SPSS histogram output into
  Word in APA format
• Be able to print out the histogram in Word

4
Definition of Histogram

• Definition of a Histogram
• A histogram is a statistical figure consisting of
  vertical bars
• A statistical figure is a drawing
• that depicts statistics

5
Explanation of a Histogram

• Explanation of a Histogram
• When analyzing frequencies the heights of the
  bars on a histogram are proportionate to the
  frequencies
• Reminder frequencies are the
• counts of how many participants
• in a study have a particular score

6
Explanation of a Histogram cont.

• Explanation of a Histogram cont
• The higher the frequency count of a particular
  score the taller the bar on the histogram will be
  (for the particular score)
• Histograms only use interval ratio variables
• Histograms only use 1 (one) variable

7
Histograms vs. Bar Graphs

• Both Histograms and Bar Graphs use vertical bars
  but
• Bar graphs
• have vertical bars that do not touch
• are created for categorical variables
• Reminder categorical variables are ordinal
  nominal
• Reminder categorical variables are not a range
  they are just a count 1 (one) variable
• Ex religions of those participating in study

8
Histograms vs. Bar Graphs

• Both Histograms and Bar Graphs use vertical bars
  but
• Histograms
• use vertical bars that touch each other
• are created for scale variables
• Reminder scale variables are interval-ratio
  (numeric)
• Reminder bars show a range of values
• Ex days absent from school of participants in
  study

9
Adding a Second Variable in SPSS

• Two Variables in SPSS
• Researchers typically collect data on several
  variables for one or more groups of participants
• Reminder a variable is a trait or characteristic
  that varies among participants in a study
• Reminder variables can be nominal, ordinal, or
  scale (interval ratio)

10
Adding a Second Variable in SPSS cont.

• Two Variables in SPSS
• To add a second variable in a
• data file in SPSS
• Use Variable View in SPSS
• Follow same procedure as adding a variable
• Make sure to name label different than other
  variables
• See Ch. 2 Holcomb /or Ch. 2 Power Point for
  additional assistance

11
Creating a Histogram in SPSS

• Making a Histogram in SPSS
• Open SPSS
• Open file click on data view
• Click on Graphs
• Use Legacy dialog for SPSS 15 to create
  histograms
• Click on Histogram

12
Creating a Histogram in SPSS cont.

• Making a Histogram in SPSS cont.
• Click on name of variable want a histogram
  created for
• Reminder One variable per histogram
• Click on top arrow-head
• Should move variable name to variable box
• Click OK (up in right top corner)
• Output with Histogram will be created

13
Example of a Histogram
Bars (count of score frequency) touch each other
Graph
Frequency count How many times participants had
that particular score for the particular variable
N 20 Sample size in study is 20 participants
Number of days absent from school of participants
in study based on reported data (a range)
Variable name
14
Normal Curve

• A Normal Curve
• A normal curve is a bell-shaped curve
• A normal curve is the normal distribution
• Shows the mean variance of the population
  having a normal distribution
• Reminder the degree to which something varies
  the average spread of a set of data
• Mean is the average score the balancing point

15
Normal Curve on a Histogram

• Why A Normal Curve on a Histogram
• A normal curve placed in a histogram depicts
  whether a histogram approximates the normal curve
• Visual representation of the normal distribution
• SPSS helps place a normal curve on a histogram to
  help determine if the distribution of scores for
  the particular variable on the histogram approach
  normal

16
Normal Curve on a Histogram

• To Place a Normal Curve on a Histogram
• Follow same steps for creating a histogram
• In Histogram dialog box click Display normal
  curve box at bottom of dialog box
• Then click ok
• Output graph of histogram should include a normal
  curve superimposed over bars

17
Example of a Histogram w/ a Normal Curve
Graph
Bell shape (or upside down U) is the normal
curve
The normal curve here shows an example of a
normal distribution
M 6.40 The average score is almost 6 a half
with a range from 0-13
Variable name
18
Difference b/w Graph Figure

• Using APA /or writing Research Report
• SPSS labels histogram as a graph
• APA social sciences call statistical drawings
• statistical figures or
• figures

19
Example of APA Formatted Histogram with Normal
Curve - as a Figure
Figure 4.2. Days absent from school with normal
distribution curve (N 20).
20
To Save Print in Word

• Save Output to Word Print
• Click on part of output you want to select
• Ex Left click mouse 1x on Histogram
• Right click on mouse
• Choose copy objects
• Open Word new document
• Right click in document
• Click paste (save print to taste)

21
Figure Tip

• Tip for Formatting Graph to Figure
• Any format changes (i.e. font, size of text) must
  be done before graph is copied to Word
• Double click on graph while still in SPSS output
• Make any changes with chart editor
• Close chart editor box to apply to graph

22
Summary

• Most researchers collect data with two or more
  variables for one or more groups of participants
• Histograms are different visually in purpose
  from Bar Charts
• Histograms represent scores of one variable from
  a particular population
• Histograms use scale (interval ratio) variables
• A Normal Curve on a histogram helps researchers
  determine if a normal distribution is present