Graphics Reference
In-Depth Information
Figure . . Doubledecker plot of the Titanic data. Survivors are highlighted. he highest survival rates
appear for the women in the crew and in the first and second classes
the corresponding variable. he stripe width is determined by the width of the tile
in the doubledecker plot. he exact combination that a specific bin represents can be
read from these labels by drawing a (virtual) vertical line from the bin through the
barsbelow.heshadesthat this linepasses throughgive the exactcombination of the
bin. he first bin of the doubledecker plot in figure . therefore is the combination
of Sex = female
Class = Crew, while the second bin shows all female passengers in
the first class, and so on.
Fluctuation Diagrams
13.3.2
In a fluctuation diagram the area of each rectangle represents the number of cases,
but the position of the bottom right corner of a bin is fixed on a grid. his display
emphasizes large bins, while small or empty bins simply vanish.
Fluctuation diagrams are constructed as follows. All of the tiles are laid out on
a rectangular grid, and each tile is initially the same size. he information on the
cell sizes is included by shrinking both the height and the width of each tile equally,
such that the remaining area is proportional to the cell size. If the original display is
quadratic,theheightandthewidthofthebinendupbeingproportionaltothesquare
root of the cell size. his makes comparisons between the widths and the heights of
the bins possible at the same time.
Figure . shows a mosaic of the College Plans data (Sewell and Shah, ). he
intelligence quotient (IQ) of a pupil is plotted versus the socioeconomic status (SES)
of his/her parents. he mosaic has the structure IQ, SES . All of the pupils who in-
tended to go to college are highlighted. In this representation, we are able to detect
three trends graphically without the need for any calculations. Let us first consider
the highlighted values. he highlighted areas grow from let to right and from top to
bottom. his type of highlighting is required in order to pick out both of the follow-
ing trends simultaneously: first, pupils with high parental SES are more likely to go
to college, and second, the percentage of college-goers also increases with IQ.
As well as these two trends, a connection between the social status of the parents
and the IQ of the pupil is visible - as the social status of the parents increases the IQ
increases, and vice versa.
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