so far we have displayed data as
averages and count now let's look at
some other statistical parameters that
we will illustrate as graphics we have
not yet shown anything about variance
and I think the first thing that one
should look into beyond averages is to
look at variance or how the data are
distributed and a good way of looking at
the distribution of data especially if
it were to be a continuous variable if
you look at histograms and if you are
interested in displaying something more
than the average maybe the median and
the quartiles then perhaps box plots
should be our choice using the teaching
evaluation data we have plotted a
histogram of teaching evaluations course
you could see that the mean score is
around 4 but then you could see very low
teaching evaluation scores not many
frequently but most frequently is to be
around the average and then you see that
some have lower teaching evaluation
scores and some have clearly
highlighting evaluation scores the
histogram approximates the normal
distribution curve essentially you have
3.99 or 4 as the mean the standard
deviation of point 55 looking at 453
records this gives you a good idea of
how your data are distributed using the
powerful SPSS graphing engine you can in
fact plot multiple histograms such that
you can see the difference between the
subgroups so here you have the
histograms overlaid for males and
females these frequent lower teaching
evaluations for females is likely to
influence the average teaching
evaluations score for females versus the
males a box plot essentially looks like
this the thick line in the box
represents the medium the top part of
the box is the third quartile the bottom
part of the box is the first quartile
the line at the bottom is the minimum
value and the line at the top is the
maximum value and the range between the
first quartile and the third quarter
note is called the interquartile range
in this graphic we see the box plots for
the age variable and we say that the
median age of males is higher than the
median age of females also the maximum
age of the males is higher than the
maximum image of females now we are
adding another dimension of tenure so
those who are tenured are plotted here
those who are not tenured applauded on
the left and the color green represents
males and the color blue represents
female instructed we can see the
differences between males and females
such that male tenured instructors are
older than male untenured instructors
whereas female tenured instructors are
younger than female untenured
instructors a pie chart is another way
of looking at your data you can see here
in this graphic that the number of
course is taught by males is larger than
the number of course is taught by female
instructors to create a histogram in
SPSS we will click on graphs chart builder
select histogram use reset to clean the
palate take the template drop it in the
palette and we're looking at teaching
evaluation scores drop here and click OK
and the histogram is readily illustrated
for a histogram with multiple groups we
click on graphs chart builder reset select the
second template and click on gender for
color and teaching evaluations score for
the histogram click OK and histogram
differentiated by gender is produced to
create a box plot we click on box plot
take the template drop it in the palette
and select gender for the x-axis and age
of the instructor as the variable for
which we can
want to compute the medians and click OK
and here is the box plot showing the
median age for female instructors and
the median age for male instructors to
have gender & tenure as the two
dimensions or a box plot you pick the
second template drop it in the canvas we
pick tenure for x-axis and gender for
the coloring and select age of the
instructor as the continuous variable
and click OK and here we have this
graphic reproduced to create a pie chart
we click on pie chart and drag it to the
palate and click on gender drop it and
then say ok and here is our pie chart
depicting that more courses were taught
by male instructors than by female
instructors
