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