introduction to spss RESEARCH METHODS & STATISTICS HANDBOOK PHẦN 2 pdf

The values from the family.sav file should now appear in the Data Editor window.. If you click on a cell when value labels are displayed in the DATA VIEW WINDOW a scroll bar will appear

SECTION II PRACTICALS

WEEK 1: Thursday October 3th

Introduction to SPSS

SPSS is the primary package for running any statistical procedures outside of the MDS packages In addition to providing outputs for various analyses, SPSS allows the user to manipulate the data in a variety of ways and to produce various graphs and figures that can be added into documents

In this practical, you will be asked to open and search through a data matrix, and enter and code data The procedure for the exercises in this practical involves going

through the steps for each analysis using the data file family.sav

Where is Family.sav?

The first thing you must do is copy family.sav from the N: drive on your computer to the M: drive (which is your own personal account) To do this you must create a folder on your M: drive into which the family.sav file will go You should be

looking at a screen with a number of icons on it In the top left-hand corner is an icon called my computer Double-click on this icon

Find the M: drive and double-click on it You should now see a window containing a number of folders Go to FILE, then NEW and choose FOLDER A new folder

should appear in the bottom of the window labelled „New Folder‟ Call your new

folder „Survey‟ and ENTER After you have done this, go to FILE and then

CLOSE

Now, within the same window double-click on your N: drive Within that drive you will see a folder with title SPSSEGS (standing for SPSS example files) Double-click

on this folder Within this folder there is a file labelled family.sav This is the file you want to copy into your „Survey‟ folder on your M: drive So, single click on

family.sav and go to EDIT and then COPY

Go back to your M: drive by shutting down the N: drive (click on the X in the right hand corner of your N: drive window) Double-click on your M: drive and double-click on the folder Survey Survey should be empty Go to EDIT and then PASTE

Now you should see the file family.sav

Exploring the Data Editor Window

Start SPSS for windows by double-clicking on the SPSS icon Once the program has been opened a window will appear in the middle of the screen with a number of

options to choose from You want to select OPEN AN EXISTING DATA

SOURCE

Go to the directory Survey in your M: drive Find the file family.sav and

double-click on it The values from the family.sav file should now appear in the Data Editor window Click on the middle button in the top right hand corner of the window to maximise the size of the window Once the file is open you will see two sheets at the

bottom of the window One is labelled DATA VIEW and the other is labelled

VARIABLE VIEW You want to stay on the data view sheet Click on the VALUE LABELS (in bold rectangle below) button on your tool bar (it is 2nd from the right) This will toggle between value labels (numeric and string (words)) Scroll through the data to answer the following questions:

1 What is the name of the last variable in the data matrix?

2 What is the case number of the last case?

3 What is the value of IDNUM for the last case?

4 What is Robert‟s date of birth?

5 What is Jack‟s marital status?

If you click on a cell when value labels are displayed in the DATA VIEW

WINDOW a scroll bar will appear to provide an indication of the options (variable

labels) used in the coding framework Using this feature, please answer the following questions:

What are the labels for CAR?

What are they for MORTGATE?

What are they for NAME? Is there a problem with NAME? What is it?

The variable view sheet

In order to view how a variable has been defined in terms of its name, variable label,

value labels and user-missing values you have to click on the sheet VARIABLE

VIEW

Please answer the following questions Do not forget to use the scroll bars on the bottom and on the right side of the variable view window to find your answers

What is the variable label for DATEBLT?

What are the values and value labels for MARSTAT? (hint: click on the grey box) What is the user-missing value for NCARS?

Click on this Sheet

Coding and Entering Data

Open up a new Data Editor window by going to FILE, then NEW and save DATA to

M: drive Below is a questionnaire regarding leisure activity and a coding scheme

Your task is to set up the Data Editor Window and then enter the data below

Leisure Activity Questionnaire

1 What is your first name?

2 What is your sex? M = male, F = female

3 What is your marital status?

1 = married 4 = widowed

2 = cohabiting 5 = divorced

3 = single 6 = separated

4 Do you watch sports? 1 = yes 2 = no 3 = do not know

5 Do you play sports? 1 = yes 2 = no 3 = do not know

6 Do you visit the seaside? 1 = yes 2 = no 3 = do not know

7 Do you go to films? 1 = yes 2 = no 3 = do not know

8 Do you go pop concerts? 1 = yes 2 = no 3 = do not know

Coding Framework

2=cohabiting 5=divorced

3 = single 6 = separated

Data

You should have a clean window in front of you (i.e., there should not be any data in the spreadsheet) You now have to set up each column of your data matrix so that you can eventually enter in your data The first column will hold IDNUM To enter

IDNUM into the data view sheet you need to go to the VARIABLE VIEW window

In fact, defining and labelling all of your variables must be done in your variable view sheet

In the first Row (horizontal) you can label and define your first variable IDNUM Using the coding framework above enter in the appropriate information Type in the

variable IDNUM under NAME The TYPE of variable is NUMERIC (you are entering a number) and under DECIMALS, using the scroll bar, choose 0 decimal places Under the heading LABELS you want to type in the definition of the

variable Make sure this definition clearly defines the variable to avoid confusion Depending upon the type of data (i.e., nominal, ordinal, ratio, or interval) you are

measuring you may have to add VALUES In the case of IDNUM (identify number)

there is only one unique number, therefore you do not have to define the variable So, under VALUES, you should have chosen none However in defining nominal data such as SEX (your third variable to enter) you would have to define male as „M‟ and female as „F‟

For IDNUM there are no missing values therefore you choose none The heading

COLUMNS will give you the opportunity to define the width of your column

Choose a width of 6 The ALIGN value allows you to determine the positioning of

your data in the cell It may be right, left or centred In the last column heading is

MEASURE This column allows you to define the type of data you are working

with With IDNUM you are working with scale data

When you define variables such as NAME (i.e., the name of the subject), you want

the TYPE of variable to be STRING, the WIDTH should be 10 (refers to the number

of characters to appear in the name) Using the coding framework below define the variable NAME

When you define variables such as sex (nominal data) you want to add value labels in

the column called VALUES If you click on the cell a value labels window will appear Across from value you should type your value M and across from the value label type male and then click on add Then you should enter F in the value box and

female in the value label box Once you have made these changes you can move back

to the DATA VIEW window and view the changes

Return to the VARIABLE VIEW window and define the numeric variable AGE in

the next row It has no decimal places, and it requires a missing value of –9 to identify cases where a response is not given To assign a user-missing value of –9 click on the

MISSING column A missing values window will appear Click on Discrete missing

values and enter –9 in the first box Set up a variable label and a value for –9 as shown in the coding scheme for your questionnaire Now, do the same for the numeric value MARSTAT in the next row This too is numeric with no decimal places, has a user-missing value of –9 and requires a variable label and several value labels as shown in the coding scheme

The remaining 5 variables also need to be defined To avoid defining each variable separately you should define the first variable WATCHSP and then copy the cells to the remaining four below To do this go to the cell you want to repeat (i.e., the value

labels) and click on EDIT, COPY and then move to the cell where you want the same definition and then go to EDIT and PASTE

When you have finished entering all of the data save it into an SPSS file by selecting

FILE, SAVE and clicking on the folder Survey in your M: drive Save the file under

any name you want (e.g., Person.sav) Exit from SPSS and log off

WEEK 2: October 10th Descriptive Statistics, Charts & Manipulating Data in the

Matrix

This practical is divided into two sections The first section is intended to familiarise you on how to run commands to calculate descriptive statistics and to graph your data The second section aims to show you how to compute re-code, filter and delete your data

Section I: Descriptive Statistics & Charts

We shall estimate descriptive statistics for the three variables: TYPACCM, DATEBLT, & NADULTS

Question: Are these variables nominal (non-ordered categories), ordinal (with ordered categories) or metrical (on a measure scale with well-defined differences between values)? Hint: The second variable is not so obvious

To run the descriptive statistics click on ANALYZE, DESCRIPTIVE STATISTICS and then FREQUENCIES In the left box there should be a list of all the variables that are present in the spreadsheet Highlight TYPACCM and click the arrow between

the boxes to move it into the box labelled „variables‟ Continue this for the other two variables A shorter route to move the variables to the „variables box‟ would be to double-click on the variables when they are in the left box - removing the variables may be accomplished in the same manner

After the three variables are in the „variables box‟, click on STATISTICS at the

bottom of the box Within the „Frequencies: Statistics‟ box there are several options

Tick the boxes for MEAN, MEDIAN & MODE on the right hand side In addition, tick the boxes for STANDARD DEVIATION (Std Deviations) & RANGE After,

click on the continue button and wait for the data to process and for the output window to appear

Answer the follow questions:

What is the most useful measure of central tendency for each of the three variables? What are the sample values?

What is the maximum value for NADULTS? Does this appear to be correct?

Now, try re-estimating the descriptive statistics for NADULTS, only this time without

the case with the unusual value Select DATA and then SELECT CASES Within

the Select Cases make sure under the „Unselected Cases‟ that the „Filtered‟ box is

ticked Then select the IF CONDITION IS SATISFIED option and click on the IF button Move the variable NADULTS to the adjacent box by either double-clicking

on it or by clicking on the variable and moving it across using the arrow

After the variable label use the calculator provided to type less than (<) the value of

the unusual variable After this hit continue and then OK to return to the spreadsheet Answer the follow questions:

Has the case with the unusual value been barred off?

Which case is it?

Now, re-run the Frequencies command for NADULTS only and record the mean,

median & mode with and without the case included

Which descriptive statistic is most affected by the unusual variable?

Graphing your Results

Histograms

Histograms are statistical diagrams that show the distribution of variables In a histogram, values are grouped together in intervals and a bar is drawn for each interval whose area is proportional to the number of cases in the interval

To generate a histogram select GRAPHS and HISTOGRAM

Then move the variable HEIGHT into the variable box In the same box, click the

„display normal curve‟ box and then hit OK

Upon examining the output window that contains the graph answer the following question:

Do you think HEIGHT has a normal distribution, or would you run other tests?

Go back to the data editor window, select GRAPHS and HISTOGRAM and run the

same command as done using the HEIGHT variable but with WEIGHT

From the histogram, would you say that the variable WEIGHT has a normal distribution or would you try other tests?

Are there any differences between the two histograms?

Scatter plots

Scatter plots show the joint behaviour of two (or more) variables in a diagram Values of one of the variables are plotted against values of another, the two variables usually being metrical A scatter plot usually shows much more about the behaviour

of the variables than descriptive statistics like correlation

Scatter plots are also drawn using the GRAPHS command Click on GRAPHS then

SCATTERPLOT then on the SIMPLE option and then click on the DEFINE

button Select WEIGHT for the Y-axis and HEIGHT for the X-axis In a scatter plot,

if one of the variables is thought to depend on the other, it is plotted on the vertical Y-axis Here, we think that weight depends on height, therefore, weight is plotted on the Y- axis

In addition, select SEX for „select markers by‟ This will allow you to identify points

on the scatter plot by sex, as males and females tend to have different heights and weights Run the command and look at the scatter plot in the chart carousel window

Can you see any difference between the males and the females in terms of heights and weights?

To edit the chart simply double-click on it Now we shall try fitting simple linear

regression lines to the data Select CHART then OPTIONS and FIT LINES (Select

Subgroups) and FIT OPTIONS Make sure linear regression has been highlighted

and then click-on „continue‟ There should be two different lines for males and females

What can you say about the slopes of the two regression lines?

Can you see any difference now between the males and the females in terms of heights and weights?

The markers used to distinguish males and females are drawn in different colours, but the difference is not very clear It will become less clear if you print out the scatter plot on a monochrome printer! Click on any marker in the plot: all markers of that sex become highlighted in black squares Then click on the icon depicting a

„crayon/pencil‟ to change the colour of the marker/symbol To change the symbol simply click on FORMAT and then MARKER There you should have several

options of changing the type and size of the symbol After making the chosen changes hit „Apply‟ and „Close‟

Editing a High Resolution Chart

Generate a high-resolution chart, a histogram, to try out some of the editing features Histograms are used for metric or quantitative variables, like AGE, which takes on values along a scale There are generally too many distinct values to make it worth drawing a bar chart Instead, the values are grouped into intervals or bands and a bar

is drawn for each interval The area of each bar is proportional to the number of cases with values in the interval

Still using family.sav select GRAPHS and then HISTOGRAM Select HWRATIO

for the variable box and click OK A histogram for HWRATIO is added to the Chart Carousel Window The histogram shows some descriptive statistics for the variable too

What are the sample mean and standard deviation for HWRATIO?