A guide to SPSS: The basics - CHESS

343 Pages·2014·2.43 MB·English

A guide to quantitative methods Almquist, Ashir & Brännström
Version 1.0
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CONTENT
INTRODUCTION ................................................................................................................................................................ .. 6
1. THE SPSS ENVIRONMENT ......................................................................................................................................... 8
1.1 General functions ........................................................................................................................................................ 9
1.2 Variable view ............................................................................................................................................................. 11
1.3 Creating a new data set ......................................................................................................................................... 13
1.4 Data view ................................................................................................................................................................ ..... 14
1.5 Syntax ................................................................................................................................................................ ........... 15
1.6 Output ................................................................................................................................................................ ........... 18
2. BASIC STATISTICAL CONCEPTS........................................................................................................................... 19
2.1 Study population and sampling ......................................................................................................................... 20
2.2 Measurement scales ............................................................................................................................................... 24
2.3 Distributions .............................................................................................................................................................. 27
3. DESCRIPTIVE STATISTICS ...................................................................................................................................... 32
3.1 Tables ................................................................................................................................................................ ........... 33
3.2 Graphs ................................................................................................................................................................ .......... 35
3.3 Measures of central tendency ............................................................................................................................. 38
3.4 Measures of variation ............................................................................................................................................ 42
4. PRODUCING DESCRIPTIVE STATISTICS IN SPSS .......................................................................................... 43
4.1 Descriptives ............................................................................................................................................................... 44
4.2 Frequency table ........................................................................................................................................................ 49
4.3 Cross table ................................................................................................................................................................ .. 55
4.4 Bar chart ................................................................................................................................................................ ...... 60
4.5 Pie chart ................................................................................................................................................................ ....... 67
4.6 Histogram ................................................................................................................................................................... 72
4.7 Scatterplot ................................................................................................................................................................ .. 77
4.8 Edit graphs ................................................................................................................................................................ . 82
5. OTHER USEFUL FEATURES IN SPSS................................................................................................................... 83
5.1 Recode ................................................................................................................................................................ .......... 84
5.2 Compute ................................................................................................................................................................ ...... 88
5.3 Select cases ................................................................................................................................................................ . 92
5.4 If ................................................................................................................................................................ ...................... 96
5.5 Weight cases .............................................................................................................................................................. 99
6. STATISTICAL SIGNIFICANCE ............................................................................................................................. 102
6.1 Hypothesis testing ................................................................................................................................................ 103
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6.2 P-values..................................................................................................................................................................... 106
6.3 Confidence intervals ............................................................................................................................................ 109
6.4 Discussion ................................................................................................................................................................ 111
7. COMPARE MEANS ................................................................................................................................................... 113
7.1 T-test: independent samples............................................................................................................................ 114
7.2 T-test: paired samples ........................................................................................................................................ 121
7.3 One-way ANOVA ................................................................................................................................................... 127
8. CHI SQUARE ............................................................................................................................................................... 134
8.1 Chi-square ................................................................................................................................................................ 135
9. CORRELATION ANALYSIS .................................................................................................................................... 140
9.1 Correlation analysis ............................................................................................................................................. 141
10. FACTOR ANALYSIS ............................................................................................................................................... 147
10.1 Factor analysis .................................................................................................................................................... 148
10.2 Cronbach’s alpha ................................................................................................................................................ 163
11. X, Y AND Z ................................................................................................................................................................ 169
11.1 X and Y ................................................................................................................................................................ .... 171
11.2 Z: confounding, mediating and moderating variables ........................................................................ 172
12. PREPERATIONS FOR REGRESSION ANALYSIS ......................................................................................... 175
12.1 What type of regression should be used? ................................................................................................ 176
12.2 Dummies ................................................................................................................................................................ 177
12.3 Standardization: z-scores ............................................................................................................................... 180
12.4 Analytical strategy ............................................................................................................................................. 184
12.5 Missing data ......................................................................................................................................................... 186
12.6 From study sample to analytical sample .................................................................................................. 189
13. LINEAR REGRESSION.......................................................................................................................................... 193
13.1 Simple linear regression ................................................................................................................................. 197
13.2 Multiple linear regression .............................................................................................................................. 213
13.3 Model diagnostics .............................................................................................................................................. 221
14. LOGISTIC REGRESSION ...................................................................................................................................... 234
14.1 Simple logistic regression ............................................................................................................................... 240
14.2 Multiple logistic regression ........................................................................................................................... 252
14.3 Model diagnostics .............................................................................................................................................. 258
15. ORDINAL REGRESSION ...................................................................................................................................... 274
15.1 Simple ordinal regression .............................................................................................................................. 279
15.2 Multiple ordinal regression ........................................................................................................................... 292
15.3 Model diagnostics .............................................................................................................................................. 299
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16. MULTINOMIAL REGRESSION .......................................................................................................................... 304
16.1 Simple multinomial regression .................................................................................................................... 309
16.2 Multiple multinomial regression ................................................................................................................. 323
16.3 Model diagnostics .............................................................................................................................................. 331
17. INTERACTION ANALYSIS .................................................................................................................................. 334

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INTRODUCTION
The purpose of this manual is to provide both basic understanding of statistical concepts (know-
why) as well as practical tools to analyse quantitative data in SPSS (know-how). We wanted to
keep the manual completely free of formulas (i.e. brain freezing statistical equations). In doing
so, we have tried to explain everything at the most elementary level and only include aspects
that are important in actual research. As such, this manual is pragmatic and research-oriented.
Hopefully, you will find it useful.

This manual consists of two parts. The first part (Chapters 1-5) concerns various aspects
concerning data management and descriptive statistics. Next, we discuss issues related to
statistical significance (Chapter 6). The following part deals with some basic types of statistical
analysis, such as t-tests, ANOVA, chi-square, correlation analysis, and factor analysis (Chapters
7-10). Then we discuss theoretical and practical dimensions of regression analysis (Chapters 11-
12) before continuing into how to actually conduct regression analysis, including interaction
analysis (Chapters 13-17).

There are two data materials used in the manual. The first is “SPSS_Data1” which is mostly based
on a hypothetical data set available through SPSS. The second is “SPSS_Data2”, which is primarily
based on several waves of data collection related to the Word Values Survey.

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General advice
Keep all your files for the course/project in the same main folder and use sub folders to
organise the files further.
Save your files under appropriate names.
Example: “Ericsson_Data_Lesson1_130603”
Keep a copy of the original file, just in case.
Example: “Ericsson _Data_Lesson1_Original”
Do not forget to continuously save your file while you work with it.
Always double-check that you have spelled values and labels correctly.
If you delete or change something by mistake, it is often possible to undo the last change by
holding down the Ctrl-key while pressing “z” on your key board.
Use syntax!

Why syntax?
The syntax is basically a text file where you can add comments and SPSS commands. The reasons
for why everyone should use the syntax function are:

• It is a way of documenting and archiving everything you have done with the data
material.
• It is easy to repeat parts or all of the analysis.
• Other people involved in the data material can easily understand what you have done
and how you have done it.
• It saves an enormous amount of time.

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1. THE SPSS ENVIRONMENT
The SPSS environment may come across as rather confusing at first, but it is actually quite
logical once you get a hang of it. In this part of the guide, we will discuss the following aspects of
the SPSS environment:

Outline
1.1 General functions
1.2 Variable view
1.3 Creating a new data set
1.4 Data view
1.5 Syntax
1.6 Output
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1.1 General functions
The Menu bar (“File”, “Edit” and so on) is located in the upper area.

In the lower left corner, two tabs are available: Data View and Variable View. When you start
SPSS, Variable View is default.

File types
SPSS uses three types of files with different functions and extensions:

Type Extension Content
Data set .sav Data and variables
Syntax .sps Commands and comments
Output .spv Results

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Options
The SPSS menu works similar to the menus in many other programs, such as Word or Excel.
Some useful options are listed below:

Option Description
Open a file Go to File\Open and choose Data, Syntax or Output. Browse your
hard drive to locate the file. Then click on Open.
Save a file Go to File\Save As. Type in a descriptive name and then click Save.
You can also choose to save only some of the variables into the new
data set by clicking Variables (before saving) and then ticking the
boxes next to the variables you want to keep.
Overwrite a file Go to File\Save.
Import a data set Go to File\Open\Data and choose the desired format next to Files of
type. Browse the file and click on Open.

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