Stacked (pyramid) bar charts for Likert Data

A while ago this question on Cross Validated showed off some R libraries to plot Likert data. Here is a quick post on replicating the stacked pyramid chart in SPSS.

This is one of the (few) examples where stacked bar charts are defensible. One task that is easier with stacked bars (and Pie charts – which can be interpreted as a stacked bar wrapped in a circle) is to combine the lengths of adjacent categories. Likert items present an opportunity with their ordinal nature to stack the bars in a way that allows one to more easily migrate between evaluating positive vs. negative responses or individually evaluating particular anchors.

First to start out lets make some fake Likert data.

**************************************.
*Making Fake Data.
set seed = 10.
input program.
loop #i = 1 to 500.
compute case = #i.
end case.
end loop.
end file.
end input program.
dataset name sim.
execute.
*making 30 likert scale variables.
vector Likert(30, F1.0).
do repeat Likert = Likert1 to Likert30.
compute Likert = TRUNC(RV.UNIFORM(1,6)).
end repeat.
execute.
value labels Likert1 to Likert30 
1 'SD'
2 'D'
3 'N'
4 'A'
5 'SA'.
**************************************.

To make a similar chart to the one posted earlier, you need to reshape the data so all of the Likert items are in one column.

**************************************.
varstocases
/make Likert From Likert1 to Likert30
/index Question (Likert).
**************************************.

Now to make the population pyramid Likert chart we will use SPSS’s ability to reflect panels, and so we assign an indicator variable to delineate the positive and negative responses.

***************************************
*I need to make a variable to panel by.
compute panel = 0.
if Likert > 3 panel = 1.
***************************************.

From here we can produce the chart without displaying the neutral central category. Here I use a temporary statement to not plot the neutral category, and after the code is the generated chart.

***************************************.
temporary.
select if Likert <> 3.
GGRAPH
  /GRAPHDATASET NAME="graphdataset" VARIABLES=Question COUNT()[name="COUNT"] Likert panel
    MISSING=LISTWISE REPORTMISSING=NO
  /GRAPHSPEC SOURCE=INLINE.
BEGIN GPL
  SOURCE: s=userSource(id("graphdataset"))
  COORD: transpose(mirror(rect(dim(1,2))))
  DATA: Question=col(source(s), name("Question"), unit.category())
  DATA: COUNT=col(source(s), name("COUNT"))
  DATA: Likert=col(source(s), name("Likert"), unit.category())
  DATA: panel=col(source(s), name("panel"), unit.category())
  GUIDE: axis(dim(1), label("Question"))
  GUIDE: axis(dim(2), label("Count"))
  GUIDE: axis(dim(3), null(), gap(0px))
  GUIDE: legend(aesthetic(aesthetic.color.interior), label("Likert"))
  SCALE: linear(dim(2), include(0))
  SCALE: cat(aesthetic(aesthetic.color.interior), sort.values("1","2","5","4"), map(("1", color.blue), ("2", color.lightblue), ("4", color.lightpink), ("5", color.red)))
  ELEMENT: interval.stack(position(Question*COUNT*panel), color.interior(Likert), shape.interior(shape.square))
END GPL.
***************************************.

These charts when displaying the Likert responses typically allocate the neutral category half to one panel and half to the other. To accomplish this task I made a continuous random variable and then use the RANK command to assign half of the cases to the positive panel.

***************************************.
compute rand = RV.NORMAL(0,1).
AUTORECODE  VARIABLES=Question  /INTO QuestionN.
RANK
  VARIABLES=rand  (A) BY QuestionN Likert /NTILES (2)  INTO RankT /PRINT=NO
  /TIES=CONDENSE .
if Likert = 3 and RankT = 2 panel = 1.
***************************************.

From here it is the same chart as before, just with the neutral category mapped to white.

***************************************.
GGRAPH
  /GRAPHDATASET NAME="graphdataset" VARIABLES=Question COUNT()[name="COUNT"] Likert panel
    MISSING=LISTWISE REPORTMISSING=NO
  /GRAPHSPEC SOURCE=INLINE.
BEGIN GPL
  SOURCE: s=userSource(id("graphdataset"))
  COORD: transpose(mirror(rect(dim(1,2))))
  DATA: Question=col(source(s), name("Question"), unit.category())
  DATA: COUNT=col(source(s), name("COUNT"))
  DATA: Likert=col(source(s), name("Likert"), unit.category())
  DATA: panel=col(source(s), name("panel"), unit.category())
  GUIDE: axis(dim(1), label("Question"))
  GUIDE: axis(dim(2), label("Count"))
  GUIDE: axis(dim(3), null(), gap(0px))
  GUIDE: legend(aesthetic(aesthetic.color.interior), label("Likert"))
  SCALE: linear(dim(2), include(0))
  SCALE: cat(aesthetic(aesthetic.color.interior), sort.values("1","2","5","4", "3"), map(("1", color.blue), ("2", color.lightblue), ("3", color.white), ("4", color.lightpink), ("5", color.red)))
  ELEMENT: interval.stack(position(Question*COUNT*panel), color.interior(Likert),shape.interior(shape.square))
END GPL.
***************************************.

The colors are chosen to illustrate the ordinal nature of the data, with the anchors having a more saturated color. To end I map the neutral category to a light grey and then omit the outlines of the bars in the plot. They don’t really add anything (except possible moire patterns), and space is precious with so many items.

***************************************.
GGRAPH
  /GRAPHDATASET NAME="graphdataset" VARIABLES=Question COUNT()[name="COUNT"] Likert panel
    MISSING=LISTWISE REPORTMISSING=NO
  /GRAPHSPEC SOURCE=INLINE.
BEGIN GPL
  SOURCE: s=userSource(id("graphdataset"))
  COORD: transpose(mirror(rect(dim(1,2))))
  DATA: Question=col(source(s), name("Question"), unit.category())
  DATA: COUNT=col(source(s), name("COUNT"))
  DATA: Likert=col(source(s), name("Likert"), unit.category())
  DATA: panel=col(source(s), name("panel"), unit.category())
  GUIDE: axis(dim(1), label("Question"))
  GUIDE: axis(dim(2), label("Count"))
  GUIDE: axis(dim(3), null(), gap(0px))
  GUIDE: legend(aesthetic(aesthetic.color.interior), label("Likert"))
  SCALE: linear(dim(2), include(0))
  SCALE: cat(aesthetic(aesthetic.color.interior), sort.values("1","2","5","4", "3"), map(("1", color.blue), ("2", color.lightblue), ("3", color.lightgrey), ("4", color.lightpink), ("5", color.red)))
  ELEMENT: interval.stack(position(Question*COUNT*panel), color.interior(Likert),shape.interior(shape.square),transparency.exterior(transparency."1"))
END GPL.
***************************************.

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1 Comment

  1. No need for SPSS – beautiful output in R #rstats | Strenge Jacke!

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