>>Dr. Barker: What we want to discuss in this
video is the depiction of qualitative variables.
We said that a couple of primary ways to depict
the count of qualitative variables would be
with a bar graph or with a pie chart, okay?
And remember again with these qualitative
variables, it’s difficult to depict them
unless we’re talking about their count in
a data set. So let’s take a look at an example
from a quality control context. Let’s say
we have an assembly for bicycles, let’s
just say. In fact, the product type here is
bicycle. And let’s say we’ve inspected
2,217 of these bicycles and there’s some
number of them, 144 of those 2,217, that has
some kind of non-conformity. Okay? So for
example, 21 of those bicycles had blisters
on the paint. Thirty-eight of them had a light
spray area on the paint of the bicycle. Twenty-two
had drips, 11 had over sprays, 47 had runs,
and then for five of those other bicycles
there was some kind of non-conformity dealing
with the paint that just fell in another category.
Okay, so 144 of those bikes had some kind
of non-conformity in the painting process.
And we’ve got a count for each one of the
occurrences of these…qualitative categories,
okay? So we have a qualitative variable here.
That qualitative variable would be called
non-conformity type, and we have six different
values that this qualitative variable can
take on. And again, they are qualitative categories
and we’ve got counts of each of those qualitative
categories. And we want to depict this graphically
somehow, okay. So we go over here in Excel,
and we’re going to use Excel just briefly
for these examples. Excel is not the very
best way to portray data, whether it’s qualitative
or quantitative, but we don’t want to get
too deep into a different…software package.
Let’s just use Excel quickly and then move
on, okay? So what we’re going to do is go
up to the “Insert” function, okay. And
here we’re going to insert – let’s first
do a bar graph. Okay, so here’s the “Insert”
function and here is a column chart. You could
represent a bar graph either as a column or
a horizontal chart, okay, row chart. But let’s
go ahead and let’s just use a 2D column
here, okay. So we’ve got this open canvas
here. We’re going to right-click in the
chart area. Excuse me, right click here, and
we’re going to select “Data,” okay?
Once we do that we’re going to enter a series,
okay, so we’re going to add. The series
name here is going to be the count, and the
series value – we’re going to delete what’s
there and we’re going to insert these. Okay,
so that’s going to be the values that we’re
going to be reading into this bar graph, okay?
Then we want categories along the horizontal
access; we don’t just want one, two, three,
and four, we actually have names for those
categories. So let’s add in our names, which
are here. Okay, and there we have it. So now
we have a bar graph depicting this data. So
I always remove the label here. If I’m going
to insert this into a document, I’m probably
going to put a label down at the bottom in
the text. You know, “Table 1” and then
give some longer descriptor of what this – or
probably Figure 1 and what this figure is
representing. I, I never like to put the label
at the top. So if you highlight on that textbook
you can just hit the delete key and remove
it. Okay, so let’s move this over a little
ways. Okay, so what do we see here? We see
that runs are most populous; others in the
“Other” category least numerous. And we
get some depictions of how these – how the
counts, how the frequency of each of these
categories relate to each other, okay? That’s
generally speaking what we get from a bar
graph, okay. The other option for us is a
pie chart. Pie charts…in the technical community,
in the data analysis community, pie charts
are viewed upon negatively. There – if you
search the Web, you can find a lot of different
alternatives to a pie chart that describes
– that describe essentially the same thing
that a pie chart can. But let’s go ahead
and just, for completeness because this is
a fundamentals class, let’s go ahead and
introduce the pie chart and how to, and how
to perform one in Excel. So we’ll go to
“Insert,” and we’ll go to insert a pie
chart icon. And let’s just insert a 2D pie
chart, okay? And so same kind of idea here:
we have an empty canvas, we’re going to
right-click on that canvas and hit “Select
Data.” And we’re going to enter in the
same series that we did previously. So here’s
the series name, the series values are in
this column right here. And let’s insert
labels that are more descriptive than just
the default categories one, two, three, four,
five and six, and let’s enter in this range
right here for the items. Okay, so that’s
it. And so now we have a pie chart – again,
I like to remove the label here. So what does
this pie chart tell us? It gives us the breakdowns
of, for example, runs versus over sprays.
We see – or pardon me, light spray. We see
Others, the smallest category, and so on,
okay? For both of these – let me move this
down here. For both of these we have some
different options on sprucing things up a
bit. If we go to the “Insert” again – pardon
me, if we go to “Designs” we’re clicking
on, we’ve clicked on the pie chart. And
we have a lot of different ways to make this
look, okay, relative to the default option.
So here, for example, we still have the same
categories but now we have labels for the
percentages of each one. Okay, that might
be a little more useful to not just get a
graphical depiction, but also a quantitative
measure. And there are different coloring
schemes. You can go over here and change colors
to different coloring scheme throughout, okay?
So a few different options for graphically
depicting this thing, okay. And likewise for
the bar graph, we have a few different options
at least color-scale wise. So for example
if this was the default…so we have labels
on each one of these giving their magnitude
of count, okay? You can have lines – horizontal
lines – going across. Change it up a little
bit: no lines going across, a completely different
shading, still numbers, and so on. Okay, so
a few different options to play around with
and of course, we can always change the color
– color scheme to whatever matches the color
scheme we’re using in the document, okay?
So again, graphically depicting qualitative
variables. We’ve got bar graphs and pie
charts depicting the same data set. This gives
us an idea of the frequency of different categories.
Same kind of idea here if we can assume that
all those categories make up the whole, okay,
and we’ve got a percentage of the whole
for each one.
