FW: Bar Graph

[Rhonda Boorman-2]

Hi ViAnn
My data is organised as one variable for pre and one variable for post, for
the same item on the survey.  The survey contained 25 items, and it was
completed once prior to the intervention and once following the
intervention.
Rhonda

-----Original Message-----
From: ViAnn Beadle [mailto:[hidden email]]
Sent: Monday, 25 August 2008 7:35 AM
To: 'Rhonda Boorman'
Cc: [hidden email]
Subject: RE: Bar Graph

How are your data organized? What do your two variables represent, different
items in a survey or one variable for pre and on variable for post? Or
something else? Data organization is everything when trying choosing the
appropriate syntax for charts.

-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
Rhonda Boorman
Sent: Sunday, August 24, 2008 3:27 PM
To: [hidden email]
Subject: Bar Graph

I am trying to create a bar graph but cannot get it to display what I want.

The data is a survey with a scale of 1 to 4, which was completed twice (pre
and post).  I want to compare the response scale for pre and post for each
item.  I want one graph for each survey item, and the columns to be the
response scale (1 to 4), divided into pre and post, and the rows will be the
frequency of responses.

I want it to look like a histogram divided by categories, but in this case
divided into 2 different variables.

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[ViAnn Beadle]

Two graphics procedures within SPSS produce "paneled" charts--GGRAPH and
IGRAPH. Both provide UIs to generate panels provided that the thing defining
the panels is a categorical variable. You, however, don't have a categorical
variable with your current structure. So the first thing to do is to
restructure the data using VARSTOCASES so that you halve the number of
variables but double your cases.

STEP 1: Restructure the data
Assume you have 2 variables xbefore and xafter and for the 1st case you have
values 1 and 3. When you restructure the file you now have 2 variables but
the variables are x and index and there are two cases that look like this:

1 1
3 2

So given your 50 variables, you'll have 26 variables, 1 for each pair and 1
for the index. Here's some syntax that first generates 10 variables and then
creates the pairs using VARSTOCASES:

input program.
loop #i = 1 to 100.
do repeat x = x1 to x10/ y=y1 to y10.
compute x=trunc(uniform(4))+1.
compute y=trunc(uniform(4)) +1.
end repeat.
end case.
end loop.
end file.
end input program.
execute.

VARSTOCASES
  /ID=id
  /MAKE v1 FROM x1 y1
  /MAKE v2 FROM x2 y2
  /MAKE v3 FROM x3 y3
  /MAKE v4 FROM x4 y4
  /MAKE v5 FROM x5 y5
  /MAKE v6 FROM x6 y6
  /MAKE v7 FROM x7 y7
  /MAKE v8 FROM x8 y8
  /MAKE v9 FROM x9 y9
  /MAKE v10 FROM x10 y10
  /INDEX=Index(2)
  /KEEP=
  /NULL=KEEP.
VALUE LABELS Index 1 "Before" 2 "After".

STEP 2 Generate the Chart
There are three procedures in SPSS that produce histograms: GRAPH, GGRAPH,
and IGRAPH. We can eliminate GRAPH because it doesn't support paneling. So
we're left with GGRAPH and IGRAPH.

A histogram assumes that have continuous data and attempts to bin the values
into buckets. But you have variables that take on only 4 values so there is
no need to bin the values into buckets. So, you can use a simple bar chart
to show the distribution. There are a few complications, however. If you
define the variable as SCALE you'll get tick values like 0.0, 0.5, ... when
you want want tick values 1, 2, 3, 4.

You can get nice tick values for your charts by defining your variable as
categorical. But this also presents some problems. You know your question
takes on values 1 to 4 but a IGRAPH doesn't know that. If you define your
variable as categorical and an individual value such as 4 has a count of 0,
the x-axis will only show 3 values. If you use IGRAPH, you have to define
the variable as SCALE and will get messy tick labels. IGRAPH presents
another problem, it panels the two charts vertically.

That leaves the GGRAPH command. You can tell the GGRAPH command that your
variable takes on 4 values so every panel for every question with have the
same number of tick marks but might not show all bars as present. GGRAPH
provides horizontal or vertical paneling. So your best solution is the
GGRAPH command.

Here's the syntax for IGRAPH for my sample data:

IGRAPH
  /VIEWNAME='Bar Chart'
  /X1=VAR(v1) TYPE=SCALE
  /Y=$count
  /PANEL=VAR(Index)
  /COORDINATE=VERTICAL
  /YLENGTH=5.2
  /X1LENGTH=6.5
  /CHARTLOOK='NONE'
  /CATORDER VAR(Index) (ASCENDING VALUES OMITEMPTY)
  /BAR KEY=ON SHAPE=RECTANGLE BASELINE=AUTO.

Note the /PANEL command which uses the Index variable to panel the two
charts.

Here's the syntax for GGRAPH for my sample data:

GGRAPH
  /GRAPHDATASET NAME="graphdataset" VARIABLES=v1 COUNT()[name="COUNT"] Index
MISSING=LISTWISE
    REPORTMISSING=NO
  /GRAPHSPEC SOURCE=INLINE.
BEGIN GPL
  SOURCE: s=userSource(id("graphdataset"))
  DATA: v1=col(source(s), name("v1"), unit.category())
  DATA: COUNT=col(source(s), name("COUNT"))
  DATA: Index=col(source(s), name("Index"), unit.category())
  GUIDE: axis(dim(1), label("Variable 1"))
  GUIDE: axis(dim(2), label("Count"))
  GUIDE: axis(dim(3), label("Index"), opposite())
  SCALE: cat(dim(1), include("1","2","3","4"))
  SCALE: cat(dim(3), include("1", "2"))
  ELEMENT: interval(position(v1*COUNT*Index), shape.interior(shape.square))
END GPL.

Note the SCALE statement in which the include function forces four
categories. Note also that the syntax explicitly specifies an axis label for
the variable. If you want a nice label, you'll have to provide it on the
GUIDE statement for axis(dim(1).

Each command charts of your original pairs of variables. But you have 25
pairs. You can create a macro to generate all the charts or just copy,
paste, and edit each command substituting the variable name and variable
label as required. You might also use the UI (Chart Builder for GGRAPH) to
create your syntax. If you do that, label your new variables and specify
values labels for values 1, 2, 3, and 4 to have it generate the include
function and label for the X axis.

This should give you something to chew on for a while.



-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
Rhonda Boorman
Sent: Sunday, August 24, 2008 3:59 PM
To: [hidden email]
Subject: FW: Bar Graph

Hi ViAnn
My data is organised as one variable for pre and one variable for post, for
the same item on the survey.  The survey contained 25 items, and it was
completed once prior to the intervention and once following the
intervention.
Rhonda

[Vi sez:] <snip/>

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