Hướng dẫn sử dụng SPSS

A Step-by-Step Guide
to Analysis and Interpretotion

Brian C. Cronk

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Notice
SPSSis a registeredtrademarkof SPSS,Inc. Screenimages@ by SPSS,Inc.
and MicrosoftCorporation.Usedwith permission.
This book is not approvedor sponsoredby SPSS.

"PyrczakPublishing"is an imprintof FredPyrczak,Publisher,
A CaliforniaCorporation.
Althoughtheauthorandpublisherhavemadeeveryeffortto ensuretheaccuracyand
for
no responsibility
completeness
of informationcontainedin thisbook,we assume
herein.Any slightsof people,
errors,inaccuracies,
omissions,
or anyinconsistency
places,or organizations
areunintentional.
ProjectDirector:MonicaLopez.
ConsultingEditors:GeorgeBumrss,JoseL. Galvan,MatthewGiblin,DeborahM. Oh,
JackPetit.andRichardRasor.
providedby CherylAlcorn,RandallR. Bruce,KarenM. Disner,
Editdrialassistance
BrendaKoplin,EricaSimmons,andSharonYoung.
Coverdesignby RobertKibler andLarryNichols.
Printedin theUnitedStates
of Americaby Malloy,Inc.
All rights
Publisher.
Copyright@2008,2006,2004,2002,1999
by FredPyrczak,
in anyform or by any
or transmitted
reserved.

No portionof thisbookmaybe reproduced
meanswithouttheprior writtenpermission
of thepublisher.
r s B N l -8 8 4 s8 5 -79 -5


Tableof Contents
Introduction
to theFifth Edition

v

What'sNew?
Audience
Organization
SPSSVersions
Availabilityof SPSS
Conventions
Screenshots
PracticeExercises
Acknowledgments'/
ChapterI
Ll
t.2
1.3
1.4
1.5
1.6
1.7
Chapter2

2.1
') ')
Chapter3

3.1
3.2
3.3
3.4
3.5
Chapter4
4.1
4.2
4.3
4.4
4.5
4.6
Chapter5

5.1
5.2
5.3
5.4

v
v
v
vi
vi
vi

vi
vii
vii

GettingStarted

I

StartingSPSS
EnteringData
DefiningVariables
LoadingandSavingDataFiles
RunningYour FirstAnalysis
ExaminingandPrintingOutputFiles
Modi$ing DataFiles

I
I
2
5
6
8

EnteringandModifyingData
VariablesandDataRepresentation
Transformation
andSelection
of Data

ll

t2

Descriptive
Statistics

l7

Frequency
Distributions
andpercentileRanksfor a singlevariable
Frequency
Distributions
andpercentileRanksfor Multille variables
Measuresof CentralTendencyandMeasuresof Dispersion
for a SingleGroup
Measures
of CentralTendency
andMeasures
of Dispersion
for MultipleGroups
StandardScores

t7
20

ll

2l
24
)7

GraphingData

29

GraphingBasics
TheNew SPSSChartBuilder
Bar Charts,Pie Charts,andHistograms
Scatterplots
AdvancedBarCharts
EditingSPSSGraphs

29
29
3l
33
36
39

Predictionand Association

4l

PearsonCorrelation Coeffi cient
SpearmanCorrelation Coeffi cient
Simple Linear Regression
Multiple Linear Regression

4l
43

45
49

u,


Chapter6

Parametric
InferentialStatistics

53

Reviewof BasicHypothesis
Testing
Single-Sample
t Test
Independent-Samples
I Test
Paired-Samples
t Test
One-WayANOVA
FactorialANOVA
Repeated-Measures
ANOVA
Mixed-Design
ANOVA
Analysisof Covariance
MultivariateAnalysisof Variance(MANOVA)

53
))
58
6l
65
69
72
75
79
8l

Chapter7

Nonparametric
InferentialStatistics

85

7.1
7.2
7.3
7.4
7.5
7.6

Chi-Square
Goodness
of Fit
Chi-SquareTestof Independence
Mann-Whitney

UTest
WilcoxonTest
Kruskal-Wallis,F/Test
FriedmanTest

85
87
.90
93
95
97

6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10

Chapter8
8.1
8.2
8.3
8.4

TestConstruction

99

Item-TotalAnalysis
Cronbach's
Alpha
Test-RetestReliability
Criterion-Related
Validiw

99
100
l0l
t02

AppendixA

Effect Size

103

AppendixB

PracticeExerciseDataSets

r 09

PracticeDataSet I
PracticeDataSet2
PracticeDataSet3

109
ll0
ll0

AppendixC

Glossary

lt3

AppendixD

SampleDataFilesUsedin Text

tt7
n7

COINS.sav
GRADES.sav
HEIGHT.sav
QUESTIONS.sav
RACE.sav
SAMPLE.sav
SAT.sav
OtherFiles

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l18
l18
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lt8

AppendixE

Informationfor Usersof EarlierVersionsof SPSS

l19

AppendixF

GraphingDatawith SPSS13.0and 14.0

t2l

tv


ChapterI

GettingStarted
Section1.1 StartingSPSS

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Startup proceduresfor SPSS will differ
slightly, dependingon the exact configurationof
the machine on which it is installed.On most
computers,you can start SPSS by clicking on
Start, then clicking on Programs, then on SPSS.
On many installations,there will be an SPSSicon
on the desktopthat you can double-click to start
the program.
When SPSS is started,you may be presentedwith the dialog box to the left, depending
on the optionsyour systemadministratorselected
for your version of the program. If you have the
dialog box, click Type in data and OK, which
will presenta blank data window.'
If you were not presentedwith the dialog
box to the left, SPSSshould open automatically
with a blank data window.
The data window and the output window provide the basic interface for SPSS. A
blank data window is shownbelow.

Section1.2 EnteringData
One of the keys to success
with SPSSis knowing how it stores
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basics of data entry with SPSS,we
will useExample1.2.1.
Example 1.2.1
A surveywas given to several
students from four different
classes (Tues/Thurs momings, Tues/Thurs afternoons,
Mon/Wed/Fri mornings, and
afternoons).
Mon/Wed/Fri
The students were asked
' Items that appearin the glossaryare presentedin bold. Italics areusedto indicatemenu items.


ChapterI GeningStarted

whether or not they were "morning people" and whether or not they worked. This
survey also asked for their final grade in the class (100% being the highest gade
possible).The responsesheetsfrom two studentsarepresentedbelow:

Response
SheetI
ID:
Dayof class:
Classtime:
Are you a morningperson?
Finalgradein class:
Do youwork outsideschool?

4593
MWF
Morning
Yes

X TTh
X Aftemoon
X No

8s%
Part{ime

Full-time

XNo
Response
Sheet2
ID:
Dayof class:
Classtime:
Are you a morningperson?

Finalgradein class:
Do vou work outsideschool?

l90l
x MwF
X Morning
X Yes

83%
Full-time
No

_
-

TTh
Afternoon
No

X Part-time

Our goal is to enterthe data from the two studentsinto SPSSfor use in future
analyses.
The first stepis to determinethe variablesthatneedto be entered.Any informaExample
tion that can vary amongparticipantsis a variablethat needsto be considered.
1.2.2liststhevariables
we will use.
Example1.2.2
ID
Dayof class
Classtime
Morningperson
Finalgrade
Whetheror not the studentworksoutsideschool
particivariablesandrowsrepresent
In the SPSSdata window,columnsrepresent
(variables)
rows

and
two
pants.Therefore,we will be creatinga datafile with six columns
(students/participants).
Section1.3 Defining Variables
Beforewe can enterany data,we must first entersomebasicinformationabout
eachvariableinto SPSS.For instance,
variablesmustfirst be givennamesthat:
o beginwith a letter;
o do not containa space.


Chapter I Getting Started

Thus, the variable name "Q7" is acceptable,while the variable name "7Q" is not.
Similarly, the variable name "PRE_TEST" is acceptable, but the variable name
"PRE TEST" is not. Capitalizationdoes not matter, but variable namesare capitalizedin
this text to make it clear when we are referring to a variable name, even if the variable
name is not necessarilycapitalizedin screenshots.
To define a variable.click on the Variable View tab at
thebottomofthema inscre e n .Th is wills h o wy o u t h e V a ri-@
able View window. To return to the Data View window. click
on the Data View tab.
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From the Variable View screen,SPSSallows you to createand edit all of the variables in your data file. Each column representssome property of a variable, and each row
representsa variable. All variablesmust be given a name. To do that, click on the first
empty cell in the Name column and type a valid SPSSvariable name. The program will
then fill in default valuesfor most of the other properties.
One usefulfunctionof SPSSis the ability to definevariableand value labels.Variable labels allow you to associatea descriptionwith each variable.Thesedescriptionscan
describethe variablesthemselvesor the valuesof the variables.
Value labelsallow you to associatea descriptionwith eachvalue of a variable.For
example,for most procedures,SPSSrequiresnumerical values.Thus, for data such as the
day of the class (i.e., Mon/Wed/Fri and Tues/Thurs),we need to first code the values as
numbers.We can assignthe number I to Mon/Wed/Friand the number2to Tues/Thurs.
To help us keep track of the numberswe have assignedto the values,we use value labels.
To assignvalue labels,click in the cell you want to assignvaluesto in the Values
column. This will bring up a small gray button (seeanow, below at left). Click on that button to bring up the Value Labelsdialog box.
--When you enter a iv*rl**
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value label, you must click L.b.f ll6rhl|
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Add after eachentry. This will
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mOVe the value and itS
associated label into the bottom section of

the window. When all labels have been
added, click OK to return to the Variable
View window.


ChapterI Gening Starred

In additionto namingand labelingthe variable,you havethe option of definingthe
variabletype. To do so, simply click on the Type, Width,or Decimals columns in the Variable View window. The default value is a numeric field that is eight digits wide with two
decimalplacesdisplayed.If your dataare more than eight digits to the left of the decimal
place,they will be displayedin scientificnotation(e.g.,the number2,000,000,000
will be
displayedas 2.00E+09).'SPSSmaintainsaccuracybeyondtwo decimalplaces,but all output will be roundedto two decimal placesunlessotherwiseindicatedin the Decimals column.
In our example,we will be usingnumericvariableswith all of the defaultvalues.
Practice Exercise
Createa data file for the six variablesand two samplestudentspresentedin Example 1.2.1.Name your variables:ID, DAY, TIME, MORNING, GRADE, and WORK. You
should code DAY as I : Mon/Wed/Fri,2 = Tues/Thurs.Code TIME as I : morning, 2 :
afternoon.CodeMORNING as 0 = No, I : Yes. Code WORK as 0: No, I : Part-Time,2
: Full-Time. Be sure you enter value labels for the different variables.Note that because
value labelsare not appropriatefor ID and GRADE, theseare not coded.When done,your
Variable View window should look like the screenshotbelow:
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Click on the Data View tab to open the data-entryscreen.Enter data horizontally,
beginningwith the first student'sID number.Enter the code for eachvariable in the appropriate column; to enterthe GRADE variablevalue,enterthe student'sclassgrade.

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Chapter I Getting Started

Thepreviousdata window canbe changedto look insteadlike the screenshot
bel*.bv clickingon the ValueLabelsicon(seeanow).In this case,the cellsdisplayvalue
labelsratherthanthe corresponding
codes.If datais enteredin this mode,it is not necessaryto entercodes,asclickingthebuttonwhichappearsin eachcell asthe
cell is selected
will presenta drop-downlist of thepredefined
lablis. You may useeithermethod,according to yourpreference.

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Instead of clicking the Value Labels icon, you may
optionallytogglebetweenviews by clicking valueLaiels under
the Viewmenu.

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Section1.4 Loading and SavingData Files
Onceyou haveenteredyour data,you will need

to saveit with a uniquenamefor later useso that you
canretrieveit whennecessary.
Loadingand savingSpSSdatafiles worksin the
sameway as most Windows-based
software.Underthe
File menu, there are Open, Save, and Save As
commands.SPSSdata files have a .,.sav" extension.
which is addedby defaultto the end of the filename.
ThistellsWindowsthatthefile is anSpSSdatafile.

I

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Save Your Data
When you save your data file (by clicking File, then clicking Save
or SaveAs to
specify a unique name),pay specialattentionto where you saveit. trrtist
systemsdefault to
the.location<c:\programfiles\spss>.You will probably want to
saveyour data on a floppy
disk, cD-R, or removableUSB drive so that you can taie the file withvou.

Load YourData
When you load your data (by clicking File, then
clicking Open, thenData, or by clicking the open file folder

icon), you get a similar window. This window lists all files
with the ".sav" extension.If you have trouble locating your
saved file, make sure you are
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looking in the right directory.


ChapterI GeningStarted

Practice Exercise
To be surethat you havemastered
saving and openingdata files, nameyour sample
datafile "SAMPLE" andsaveit to a removable

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Data Transform Annhze @al

storagemedium. Once it is saved,SPSSwill display the name of the file at the top of the
data window. It is wise to save your work frequently,in caseof computer crashes.Note
that filenamesmay be upper- or lowercase.In this text, uppercaseis usedfor clarity.
After you have saved your data, exit SPSS (by clicking File, then Exit). Restart
SPSSand load your databy selectingthe "SAMPLE.sav"file you just created.

Section1.5 RunningYour First Analysis
Any time you open a data window, you can mn any of the analysesavailable.To
get started,we will calculatethe students'averagegrade.(With only two students,you can

easily checkyour answerby hand,but imaginea data file with 10,000studentrecords.)
The majority of the available statistical tests are under the Analyze menu. This
menu displaysall the optionsavailablefor your versionof the SPSSprogram (the menusin
this book were createdwith SPSSStudentVersion 15.0).Otherversionsmay haveslightly
different setsof options.

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To calculatea mean (average),we are asking the computerto summarizeour data
set. Therefore,we run the commandby clicking Analyze, then Descriptive Statistics,then
Descriptives.
This brings up the Descriptives dialog
box. Note that the left side of the box containsa
OAY
list of all the variablesin our data file. On the right
.Sr ql

is an area labeled Variable(s), where we can
3s,l
specifythe variableswe would like to use in this
particularanalysis.
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Chapter I Getting Started

l:rt.Ij
We want to compute the mean for the
variable called GRADE. Thus, we need to select
the variable name in the left window (by clicking
;F* |
on it). To transfer it to the right window, click on
-t:g.J
the right arrow between the two windows. The
-!tJ
arrow always points to the window opposite the f- Smdadr{rdvdarvai&
PR:l
highlighted item and can be used to transfer
selectedvariablesin either direction.Note that double-clickingon the variable name will
also transfer the variable to the opposite window. Standard Windows conventions of
"Shift" clicking or "Ctrl" clicking to selectmultiplevariablescan be usedas well.
When we click on the OK button, the analysiswill be conducted,and we will be
readyto examineour output.

in

m

Section1.6 Examiningand PrintingOutput Files
After an analysis is performed, the output is
placed in the output window, and the output window
becomesthe active window. If this is the first analysis
you have conducted since starting SPSS, then a new
output window will be created.If you have run previous analyses
and savedthem,your

outputis addedto theendof yourpreviousoutput.
To switchbackandforthbetweenthedata window andtheoutput window,select
thedesiredwindowfrom the Windowmenubar(seearrow,below).
The output window is split into two sections.
The left sectionis an outlineof the
(SPSS
"outline
output
refersto this asthe
view").Theright sectionis theoutputitself.
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The sectionon the left of the output window provides an outline of the entire output window. All of the analysesare listed in the order in which they were conducted.Note
that this outline can be used to quickly locate a sectionof the output. Simply click on the
sectionyou would like to see,and the right window will jump to the appropriateplace.


ChapterI GeningStarted

Clicking on a statisticalprocedurealso selectsall of the output for that command.
By pressingtheDeletekey, that outputcan be deletedfrom the output window. This is a
quick way to be sure that the output window containsonly the desiredoutput. Output can
also be selectedand pastedinto a word processorby clicking Edit, then Copy Objecls to
copy the output.You can then switch to your word processorand click Edit, thenPaste.
To print your output, simply click File, then Print, or click on the printer icon on
the toolbar. You will have the option of printing all of your output or just the currently selected section. Be careful when printing! Each time you mn a command, the output is
addedto the end of your previous output. Thus, you could be printing a very large output
file containinginformation you may not want or need.
One way to ensurethat your output window containsonly the resultsof the current
commandis to createa new output window just before running the command.To do this,
click File, then New, then Outpul. All your subsequentcommandswill go into your new
output window.
Practice Exercise
Load the sampledata file you createdearlier (SAMPLE.sav). Run the Descriptives
command for the variable GRADE and print the output. Your output should look like the
exampleon page7. Next, selectthe data window and print it.

Section1.7 ModifyingData Files
Once you have createda data file, it is really quite simple to add additional cases
(rows/participants)
or additionalvariables(columns).ConsiderExample1.7.1.

Example1.7.1
Two morestudents
provideyou with surveys.
Theirinformationis:
ResponseSheet3
ID:

Day of class:
Classtime:
Are you a morningperson?
Final gradein class:
Do you work outsideschool?

ResponseSheet4
ID:
Day of class:
Classtime:
Are you a morning person?
Final gradein class:
Do you work outsideschool?

8734
MWF
Morning
Yes

X TTh
Afternoon
XNo

80%
Part-time

Full-time
No

1909

X MWF
X Morning
X Yes
73%
Full+ime
No

TTH
Afternoon
No
X

Part-time


Chapter I Getting Started

To add thesedata, simply place two additionalrows in the Data View window (after loading your sampledata).Notice that as new participantsare added,the row numbers
becomebold. when done,the screenshouldlook like the screenshothere.
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4593.00 Tueffhu aternoon
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85.00
No
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Yes
83.00 Part-Time
8734.00 Tue/Thu mornrng
No
80,00
No
1909.00MonAfVed/ mornrng
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New variables can also be added.For example, if the first two participantswere
given specialtraining on time management,and the two new participantswere not, the data
file can be changedto reflect this additionalinformation.The new variable could be called

TRAINING (whether or not the participant receivedtraining), and it would be coded so
that 0 : No and I : Yes. Thus, the first two participantswould be assigneda "1" and the
Iast two participantsa "0." To do this, switch to the Variable View window, then add the
TRAINING variable to the bottom of the list. Then switch back to the Data View window
to updatethe data.
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85.0u
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Adding data and adding variablesare just logical extensionsof the procedureswe
used to originally createthe data file. Save this new data file. We will be using it again
later in the book.


Chapter I Getting Started

Practice Exercise
Follow the exampleabove(whereTRAINING is the new variable).Make the
modifications
to your SAMPLE.savdatafile andsaveit.

l0


Chapter2

EnteringandModifying Data
In Chapter 1, we learnedhow to createa simple data file, save it, perform a basic
analysis,and examine the output. In this section,we will go into more detail about variablesand data.

Section2.1 Variablesand DataRepresentation
In SPSS,variablesare representedas columns in the data file. Participantsare representedas rows. Thus, if we collect 4 piecesof information from 100 participants,we will
have a data file with 4 columnsand 100 rows.
Measurement Scales

There are four types of measurementscales:nominal, ordinal, interval, and ratio.
While the measurementscalewill determinewhich statisticaltechniqueis appropriatefor a
given set of data, SPSSgenerally does not discriminate.Thus, we start this section with
this warning: If you ask it to, SPSSmay conduct an analysis that is not appropriatefor
your data.For a more completedescriptionof thesefour measurementscales,consultyour
statisticstext or the glossaryin Appendix C.
Newer versionsof SPSS allow you to indicate which types of
Measure
data you have when you define your variable. You do this using the
Measurecolumn. You can indicateNominal, Ordinal, or Scale(SPSS @Nv
doesnot distinguishbetweeninterval and ratio scales).
f $cale
.sriltr
Look at the sampledata file we createdin Chapter l. We calcur Nominal
lated a mean for the variable GRADE. GRADE was measuredon a ra-

summarystatistic(assumingthat the distribution
tio scale,andthe mean is an acceptable
is normal).
We could have had SPSScalculatea mean for the variableTIME insteadof
here.
GRADE.If we did, we wouldgettheoutputpresented
The outputindicatesthat the averageTIME was 1.25.Rememberthat TIME was
coded as an ordinal variable ( I =
m or ni ngcla ss,2-a fte rnoon
trlllql eilr $l-g
class).Thus, the mean is not an *lq]eH"N-ql*l
appropriatestatisticfor an ordinal
:* Sl astts
.l.:D

gtb
scale,but SPSScalculatedit any:$sh
way. The importance of considering the type of data cannot be
overemphasized. Just because
ht6x0tMn
SPSS will compute a statistic for
you doesnot mean that you should
.6M6.ffi

ll

$arlrba"t S#(|
LS
a

2.qg

Lt@


Chapter2 Enteringand Modifying Data

use it. Later in the text, when specificstatisticalproceduresare discussed,the conditions
underwhich they are appropriatewill be addressed.
Missing Data
Often, participantsdo not provide completedata.For some students,you may have
a pretestscore but not a posttestscore.Perhapsone studentleft one question blank on a
survey,or perhapsshe did not stateher age.Missing data can weakenany analysis.Often,
a singlemissingquestioncan eliminatea subject
from all analyses.

ql
total
If you have missing data in your data
2.00
2.Bn
4.00 set, leave that cell blank. In the example to
3.00
1.0 0
4.00 the left, the fourth subject did not complete
Question2. Note that the total score(which is
4.00
3.00
7.00 calculatedfrom both questions)is also blank
becauseof the missing data for Question 2.
2.00
SPSS representsmissing data in the data
1 .0 0
2.UB
3.00 window with a period (althoughyou should
not enter a period-just leave it blank).

Section2.2 Transformationand Selectionof Data
We oftenhavemoredatain a datafile thanwe wantto includein a specificanalysis.For example,our sampledatafile containsdatafrom four participants,
two of whom
receivedspecialtrainingand two of whom did not. If we wantedto conductan analysis
usingonly the two participants
who did not receivethe training,we wouldneedto specify
theappropriate
subset.
Selectinga Subset

F|! Ed vl6{ , O*. lr{lrfum An*/& e+hr
O*fFV{ldrr PrS!tU6.,.
CoptO.tafropc,tir3,..

t'llitl&JE

il :id

l,j.l,/r,:irrlrr! lif l ll:L*s,,.

Hh.o*rr,.,
Dsfti fi*blc Rc*pon$5ct5,,,

(

We can use the SelectCasescommandto specify
a subset of our data. The Select Cases command is
located under the Data menu. When you select this
command,the dialog box below will appear.
q*d-:-"-- "-"""-*--*--**-""*-^*l
6 Alce
a llgdinlctidod
,r l

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c

You can specify which cases(participants) you want to select by using the selection criteria, which appearon the right side of
the SelectCasesdialog box.

-:--J
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C6ttSldrDonoan!.ffi

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t2

aar I c-"rl x* |

i:


Chapter2 Enteringand Modifying Data

By default,All caseswill be selected.The most common way to selecta subsetis
to click If condition is satisfied, then click on the button labeledfi This will bring up a
new dialog box that allowsyou to indicatewhich casesyou would like to use.
You can enter the logic
used to select the subset in the
upper section. If the logical
statement is true for a given
case, then that case will be
U;J;J:.1-glL1 E{''di',*tI
'J-e.l-,'JlJ.!J-El[aasi"-Eo,t----i
,
selected.If the logical statement
is false. that case will not be
0 U IAFTAN(r"nasl
,Jl _!JlJ
selected.For example, you can
sl"J=tx
-s*t"lBi!?Blt1trb :r
select all casesthat were coded
?Ais"I c'-t I Ht I
as Mon/Wed/Fri by entering the
formula DAY = I in the upperright part of the window. If DAY is l, thenthe statementwill be true,and SPSSwill select
the case.If DAY is anything other than l, the statementwill be false, and the casewill not
be selected.Once you have enteredthe logical statement,click Continue to return to the
SelectCasesdialog box. Then,click OK to returnto the data window.
After you have selectedthe cases,the data window will changeslightly.
The casesthat were not selectedwill be markedwith a diagonalline through the
casenumber. For example,for our sampledata, the first and third casesare not
selected.only the secondand fourth casesare selectedfor this subset.

ilqex4q lffiIl,?,l*;*"'=

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MORNING ERADE WORK TRAINING
4533.m Tueffhui affsrnoon
No
ffi.m
Na
Yes Not Selected
1901.m
MpnMed/i mornino
Yss
83,U1Fad-Jime
Yes
Splacled
6h4lto TuElThu
No
m.m
. morning

No
No Not Selected
ieifrfft MonA/Ved/1morning
Yes
ru.mPart-Time
No
. -..- ^,-.-.*.*..,--

1

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I

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TIME

ID

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t

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!LJ\ii. vbryJv,itayss 7

I

. *-JI

fsPssProcaesaFrcady

i

*] ,1,

An additional variable will also be createdin your data file. The new variable is
called FILTER_$ and indicateswhethera casewas selectedor not.
If we calculatea mean
DescripthreStailstics
GRADE using the subset we
just selected,we will receive
std.
N
Minimum Maximum M e a n
Deviation
the output at right. Notice that
UKAUE
2
73.00
83.00 78.0000 7 . 0 7 1 1
we now have a mean of 78.00 Va lid N
2
IliclwisP'l
with a samplesize (M) of 2 insteadof 4.

l3

1

'l


Chapter2 Enteringand Modifying Data

Be careful when you selectsubsets.The subsetremains in ffict until you run the
commandagain and selectall cases.You can tell if you have a subsetselectedbecausethe
bottom of the data window will indicatethat a filter is on. In addition, when you examine
your output, N will be less than the total number of recordsin your data set if a subsetis
selected.The diagonal lines through some caseswill also be evident when a subsetis selected.Be careful not to saveyour data file with a subsetselected,as this can causeconsiderableconfusionlater.
Computing a New Variable
SPSScan also be used
to compute a new variable or nh E* vir$, D.tr T|{dorm
manipulateyour existing vari*lslel EJ-rlrj -lgltj{l -|tlf,l a*intt m eltj I
ables. To illustrate this, we
will create a new data file.
This file will contain data for
four participants and three
variables (Ql, Q2, and Q3).
The variables represent the
points each
number of
l* ,---- LHJ
participant received on three
{#i#ffirtr!;errtt*;
different questions.Now enter
the data shown on the screen to the right. When done, save this data file as
"QUESTIONS.sav."We will be usingit againin laterchapters.
I TrnnsformAnalyze Graphs Utilities Whds

Rersdeinto5ameVariable*,,,
intoDffferant
Varlables.
Racodo

,,
Ar*omSicRarode,,.
Vlsual
8inrfrg,..

After clicking the Compute Variable
command, we get the dialog box at
right.
The blank field marked Target
Variable is where we enter the name
of the new variable we want to create.
In this example, we are creating a
variable called TOTAL, so type the
word "total."
Notice that there is an equals
sign between the Target Variable
blank and the Numeric Expression
blank. These two blank areas are the

Now you will calculatethe total score for
eachsubject.We could do this manually,but if the
data file were large, or if there were a lot of
questions,this would take a long time. It is more
efficient (and more accurate) to have SPSS
compute the totals for you. To do this, click
Transform and then click Compute Variable.

,

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gl
w
ca

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lij -!CJ:l Jslcl
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Chapter2 Enteringand Modifying Data

iii:Hffiliji:.:

. i . i> t

i-Jr:J::i
l:j -:15
tJ -tJ-il
is:Jlll

two sides of an equation that SPSS
will calculate.For example,total : ql
+ q2 + q3 is the equation that is
entered in the sample presentedhere
(screenshot
at left). Note that it is possible to create any equation here
simply by using the number and
operational keypad at the bottom of
the dialog box. When we click OK,
SPSSwill createa new variablecalled
TOTAL and make it equalto the sum
of the threequestions.
Save your data file again so
that the new variablewill be available

for future sessions.

ii"alCt

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--q*J

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x*

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t::,,

- ltrl-Xl

Eile gdit SEw Qata lransform $nalyza 9aphs [tilities Add'gns Sindow Help

3.n0

4,n0

3.0n

10.00

4.00

31..........;.
2.oo
l
I

41

1.0 0 1

.:1

l-'r
--i-----i

2.oo
3 0 01

il
I

i
, l, l\qg,t_y!"*_i Variabte
ViewJ

Recodinga Variable-Dffirent

lit
W*;

r ljl

Variable

SPSS can create a new
variable based upon data from
another variable. Say we want to
split our participantson the basisof
their total score.We want to create
a variablecalled GROUP, which is
coded I if the total score is low
(lessthan or equal to 8) or 2 if the
total score is high (9 or larger). To
do this, we click Transform, then
Recodeinto Dffirent Variables.

F{| [dt

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Data j Trrx&tm

,-.lu l,rll r-al +.

---.:1.l{
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4.00

Analrra

vdiouc','
conp$o
Cd.nVail'r*dnCasas.,,
-o ..* * ^ c- - u - r - c

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U*dFhn|ro,,.

2.00

i.m
Racodrlrto 0ffrror* Yal

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Rid&c l4sitE V*s.,.
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Ch a p te 2
r En te ri n ga n d Mo d i fy i n gD ata

This will bring up the
Recode into Different Variables
dialog box shown here. Transfer
the variable TOTAL to the middle
blank. Type "group" in the Name
field under Output Variable.Click
Change,and the middle blank will
show that TOTAL is becoming
GROUP.as shownbelow.

til

ladtnl c€ rlccdm confbil

-'tt"

rygJ**l-H+ |

I

NtnHbvli|bL-lo|rnrV*#r

To help keep track of variablesthat have
been recoded, it's a good idea to open the
t *.!*lr
Variable View and enter "Recoded" in the Label rr&*ri*i*t
column in the TOTAL row. This is especially ;rln
I r-":-'-'1**
useful with large datasets which may include i T I r nryrOr:frr**"L
many recodedvariables.
,fClick Old andNew Values.This will bring i c nq.,saa*ld6lefl;
Fup the Recodedialog box. In this example,we
have entered a 9 in the Range, value through
HIGHEST field and a 2 in the Value field under
New Value.When we click Add, the blank on the ,.F--*-_-_-_____
right displaysthe recodingformula. Now enter an :I "a *r***o
lrt*cn*r
I I nni.
8 on the left in the Range, LOWEST through rT..".''..."...value blank and a I in the Value field under New I ir:L-_t'
Value. Click Add, then Continue.Click OK. You l6; F i4i'|(tthah*
T &lrYdd.r*t
will be redirectedto the data window. A new I " n *'L,*l'||.r.$,
: r----**-:
variable (GROUP) will have been added and ; r {:ei.*
gf-ll
codedas I or 2, basedon TOTAL.
lirli

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Flc Ed Yl.ly Drt! Tr{lform
{*!c

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Chapter3

DescriptiveStatistics
ln Chapter2, we discussed

manyof the optionsavailablein SPSSfor dealingwith
our data.The procedures
usedto describe
data.Now we will discusswaysto summarize
andsummarizedataarecalleddescriptivestatistics.
Section3.1 FrequencyDistributions and PercentileRanks
for a SingleVariable
Description
The Frequencies
commandproducesfrequencydistributionsfor the specifiedvaripercentages,
ables.The outputincludesthe numberof occurrences,
valid percentages,
and
and the cumulativepercentages
cumulativepercentages.
The valid percentages
comprise
asmissing.
only thedatathatarenot designated
TheFrequencies
commandis usefulfor describingsampleswherethe meanis not
useful(e.g.,nominalor ordinal scales).
It is alsousefulasa methodof gettingthefeelof
your data.It providesmoreinformationthanjust a meanandstandarddeviationandcan
be usefulin determiningskewandidentifyingoutliers.A specialfeatureof the command
percentileranks.
is its abilityto determine
Assumptions
Cumulativepercentages
and percentilesare valid only for datathat are measured

on at leastan ordinal scale.Because
the outputcontainsoneline for eachvalueof a variable,thiscommandworksbeston variableswith a relativelysmallnumberof values.
Drawing Conclusions
TheFrequencies
outputthatindicatesboththenumberof cases
commandproduces
in the sampleof a particularvalueandthe percentage
of caseswith that value.Thus,conclusionsdrawnshouldrelateonly to describingthe numbersor percentages
of casesin the
regardingthe cumulativepersample.If the dataareat leastordinalin nature,conclusions
centageand/orpercentilescanbe drawn.
.SPSSData Format
The SPSSdatafile for obtainingfrequencydistributions
requiresonly onevariable,
andthatvariablecanbeof anytype.

tt


C h a p te 3
r D e s c ri p ti v e
Sta ti s ti c s

Creating a Frequency Distribution
To run the Frequer?ciescommand,
click Analyze, then Descriptive Statistics,
I
slsl}sl &99rv
i:rl.&{l&l&l
@

then Frequencies.(This example uses the i 1 r mpg
}
Disbtlvlr...
cdrFrb'l{tirE
i 18
N
Erpbr,..
CARS.savdata file that comeswith SPSS.
croac*a,..
Rrno,.,
It is typically located at F.Pt'lok,.,
aaPUs,.,
Fi les\SPS
S\Cars.
sav>.)
This will bring up the main dialog r5117gl
box. Transfer the variable for which you
would like a frequencydistributioninto the
Variable(s)blank to the right. Be surethat
xl
tables option is
the Display
MilesperGallonlm r
q ! l checked.Clickfrequency
OK to receiveyour output.
/Erqlr,onispUcamr
that
the dialog boxes in
/ Hurepowor[horc

Note
dv*,id"w"bir 1|ut
jq? | newer versions of SPSS show both the
d t!rc toAceileistc
.f"tq I type of variable(the icon immediatelyleft
dr',Ccxr*yol Orbin[c
. He_l of the variable name) and the variable
labels if they are entered. Thus, the
l7 Oisgayhequercytder
variable YEAR shows up in the dialog
box as Model Year(modulo I0).
sr**i,1..1
rry*,:.
I
f*:.,. I
Output for a Frequency Distribution
The output consistsof two sections.The first sectionindicatesthe numberof records with valid data for eachvariableselected.Recordswith a blank scoreare listedas
missing.In this example,the datafile contained406 records.Notice that the variablelabel
is ModelYear (modulo100).
The second section of the output contains a
statistics
cumulative frequency distribution for each variable
Wse lected.A tth e topof t h e s e c t io n , t h e v a ria b le la b e lis
*
oo?
y.1"1 |
| given. The output iiself consistsof five columns.The first
|
Missing
t I

I
I
Jolumnliststhi valuesof the variablein sortedorder.There
is a row for eachvalue of your variable,
and additional rows are added at the
bottom for the Total and Missing data.
The secondcolumn gives the frequency
of eachvalue,includingmissingvalues.
The third columngivesthe percentage
of
all records (including records with
missingdata) for eachvalue.The fourth
column, labeled Valid Percenl, gives the
percentage
of records(without including
records with missing data) for each
value. If there were any missingvalues,
these values would be larger than the
valuesin column threebecausethe total

Modol Yo.r (modulo 100)
Cumulativs
Pcr ce n l

34

vatE

72
73

74
75
76
77

28
40
27
30
34
28

79
80
81
82
Total
Missing 0 (Missing)
Total

29
29
30
31
405
1
406

r8

I 4
7.1
6.9
9.9
6.7
8.4
6.9
8.9
7.1
7.1
7.4
7.6
99.8
100.0

Valid P6rc€nl
I 4

7.2
6.9
9.9
6.7
7.4
8.4
6.9
8.9
f.2

7.2
7.4

7.7

100 .0

E4
15.6
22.5
32.3
39.0
46.4
54.8
61.7
70.6
77.8
84.9
92.3
| 00.0


Chapter3 DescriptiveStatistics

numberof recordswould have beenreducedby the numberof recordswith missing values.
The final column gives cumulative percentages.Cumulative percentagesindicate the percentageof records with a score equal to or smaller than the current value. Thus, the last
value is always 100%. These values are equivalentto percentile ranks for the values
listed.

D eterm ining P ercenti Ie RanlThe Frequencies command can be
used to provide a number of descriptive
Sfndr*Pi*rcsnr

statistics,as well as a variety of percentile
SHslsp{rierltuso
(including quartiles, cut points, and
values
/v***v*$t*(ttu
YI
/lino toaccrbrar
!rydI scorescorrespondingto a specificpercentile
$1C**{ry o{Origr[c
|*"1 rank).
To obtain either the descriptiveor
lT Oirpbar
frcqlcreyttblce
percentile functions of the Frequencies
command,click the Statisticsbutton at the
frfix*... I
bottomof the main dialog box. Note that the
Central Tendencyand Dispersior sectionsof this box are useful for calculatingvalues,
suchas the Median or Mode. which cannotbe calculatedwith the Descriptiyescommand
(seeSection3.3).
:,,.

tril

Mla pa Galmlm3

This brings up the Frequencies:
Statisticsdialog box. Check any additional
desiredstatisticby clicking on the blank next
to it. For percentiles, enter the desired

percentile rank in the blank to the right of
the Percentile(s)label. Then, click Add to add
it to the list of percentiles requested.Once
you have selectedall your requiredstatistics,
click Continue to return to the main dialog
box. Click OK.

tr Ourilr3
F nrs**rtd!i*

c{q I
*g"d I

I
,crnqo,p, i

Hdo I

f- Vdrixtgor0mi&ohlr
Oi$.r$pn "
l* SUaa**
n v$*$i
I* nmgc

f Mi*n n
|- Hrrdilrtl
l- S"E.mcur

0idthfim'
t- ghsrurt

T Kutd*b

Outputfor Percentile Ranl
Statistics
ModelYear (modulo100
N
Vatid
Missing
Percentiles 25
50
75
80

xl

PscdibV.lrr

405
1
73.00
76.00
79.00
80.00

The Statistics dialog box adds on to the
previous output from the Frequenciescommand.The
new sectionof the output is shown at left.
The output containsa row for each piece of
information you requested.In the example above, we

checkedQuartiles and asked for the 80th percentile.
Thus, the output contains rows for the 25th, 50th.
75th,and 80th percentiles.

l9


Ch a p re ,1
r D e s c ri p tier S ta ti s ti cs

Practice Exercise
UsingPracticeDataSet I in AppendixB, createa frequencydistributiontablefor
the mathematics
skills scores.Determine
the mathematics
skills scoreat which the 60th
percentile
lies.
section 3.2 FrequencyDistributions and percentileRanks
for Multiple Variables
Description
The Crosslabscommandproducesfrequencydistributionsfor multiple variables.
The outputincludesthenumberof occurrences
of eachcombinationof levelJof eachvariable.It is possibleto havethecommandgivepercentages
for anyor all variables.
The Crosslabscommandis usefulfor describingsampleswherethe mean is not
useful(e'g.,nominalor ordinal scales).
It is alsousefulasa methodfor gettinga feelfor
your data.
Assumptions

Becausethe outputcontainsa row or columnfor eachvalue of a variable.this
command
worksbeston variables
with a relativelysmallnumberof values.
,SPSSData Format
The SPSS data file for the Crosstabs
lnalyzc Orphn Ut||Uot
commandrequirestwo or more variables.Those I
)
RcF*r
variablescanbe of anytype.
Runningthe CrosstabsCommand

This exampleusesthe SAMpLE.sav
data
file, which you createdin Chapter l. To run the
procedure, ctick Analyze, then Descriptive
Statistics,then Crosstabs.This will bring up ttt.
main Crosstabsdialog box, below.

i,

r---r

Ror{.}
ftr;;ho.-

l rJ I

.;lm&!

T€K I
'-l
ryq I

(orprycrllcEnr
)
G*ncral
llrgar Flodcl )
,
)
;ilffi;
)
chrfy
DttaRcd.Etbn )
)
scah

The dialog box initially lists all variables on the left and contains two blanks labeled Row(s) and Column(s). Enter one variable (TRAINING) in the Row(s) box. Enter the
second (WORK) in the Column(s) box. To
analyze more than two variables, you would
enter the third, fourth, etc., in the unlabeled
area(ust under theLayer indicator).

20