>> So here we are in SPSS.
I have created a junk data
set just to help
illustrate how we can
compute variables
or compute
new variables using
the values from
existing ones.
This is a pretty
straightforward process.
It looks a little bit
different than things
that we've done
before or other
ways that we're
going to be using
SPSS in this course.
So it might look a
little bit different,
but it is pretty
straightforward and
pretty easy once you
know how to do this.
So the first
thing that we'll
do is go to Transform,
and then the
first option we
have there is
compute variable.
So click on that. We get
this new window
that pops up.
The first thing
that we really want
to look at is in
the top left,
and that's this target
variable window.
Basically what
the computer
is asking you is to create
a name for the
new variable
that you're going
to be computing.
This name needs
to be unique,
it's one that can't
have spaces in it,
and it should avoid
special characters.
But, in this case,
what I like to
do is include
some piece of
information in there
in the naming
convention I use that
helps me know what this is
just by looking at it.
So what we're going
to be doing is
we're going to be
summing items 1,
2, 3, 4, 5,
and 6 together, adding
those together.
So an easy way
to do that is
just to put sumofitems.
That way, when I look at
this new variable
once it's generated,
I know that that's
the variable
that I really want
to be working
with or running
my tests on
because that contains
the information from
the other ones.
You can click on
Type & Label.
The label is the more
drawn-out explanation.
That's one that
you can include
additional characters or
spaces and special
characters.
In our case, I'm
going to put this is
the sum of items
1 through 6.
And that way I know that
that is going to give me
a more drawn-out
explanation
of what this
variable includes.
We know this is
going to be numeric.
So click Continue.
The next thing we're
going to look at
is this numeric
expression box.
And will actually
come back
to this in just a minute,
but this is where you're
going to be doing most
of the work when you're
computing a variable.
What you'll want
to go to next
is this function
group area.
So I'm going to
click on All.
And you notice right
below it we've
got these functions
and special variables,
and this popped up
when I clicked on All.
This has a whole bunch of
different pre-existing
functions,
so you don't need to
reinvent the wheel,
you can basically use
these pre-existing
functions to
help you compute
this new variable.
I'm going to go
down to sum,
and these are in
alphabetical order,
so it's pretty
easy to find.
Here we have sum, and
when I click on sum,
you'll notice
that this box on
the left populated
with some text.
This box is actually
pretty useful.
So the first thing
it shows you is
an example of what
this expression
is going to be.
And our expression
sounds like
a really fancy term.
If you've ever
used a formula
in Excel, it's
basically that.
It's telling the computer
what it needs to do.
In this case,
just like Excel,
we've got the word sum,
which tells the computer
it's going to be
summing different
values together,
and then in parentheses,
immediately after that,
we have different
variables
that are separated
by a comma,
and that's what tells the
computer to add x, y,
and z things
together to create
a new variable or
compute a new variable.
This also provides
additional extra
content here,
but we don't need to
worry about that.
I found this is
helpful if you
are stuck or something
isn't working right.
So we've got sum selected,
we're going to be
summing the items of 1,
2, 3, 4, 5, and
6 together.
We've got that selected.
So the next thing you do
is click this up arrow,
which basically takes
that pre-existing function
and it kicks it up
to this numeric
and expression box.
The next thing that
we're going to do,
we've already told
the computer
that we're going
to sum different
variables together,
we need to tell it which
variables to sum together.
So the easy way
to do this is to
click on the first
item that you
want to include,
and you'll notice
that this arrow
switch sides from pointing
to the left to
pointing to the right,
click over 1,
and we've already
moved over item 1.
What you need to be
careful of is that you
always have a comma
after each variable,
except for the last one.
So a comma is
already here,
but what I usually do
is I just hit a comma,
I go to item 2,
kick that over, comma,
item 3, kick that over,
comma, item 4,
kick that over,
comma, item 5,
kick that over, comma,
item 6, kick that over.
Now, we know that item 6
is the last one we have,
the last variable
we're including,
so what we're
going to do is
just delete out
that question mark,
we're going to delete
out that last comma,
and then if we read
through this real quick
just to make sure we
don't have any problems,
we've got creating
sumofitems,
this is going to
be the sum of
item 1, 2, 3,
4, 5, and 6,
and what we're going
to do now is click OK.
An output window pops
up and it basically tells
you what the computer did.
It computed the
sum of items,
which was the
sum of item 1,
2, 3, 4, 5, and 6,
it gives us the
variable label,
it gives us that
descriptive text I put in.
I'm just going to
minimize this window,
and if we look back here,
you might notice that
there's this new column,
this new variable,
that sumofitems,
that wasn't there
when we started,
and that's because
SPSS computed that.
And if we add
these together,
if you add each row,
we've got 1, 2, 1, 3, 5,
1, that adds to 13,
5, 1, 2,
3, 5, 1 adds to 17.
So it's done that
math for us.
We didn't have to
manually do it.
I know, yes, it'd
be pretty easy to
manually do this
for 10 cases,
but if you have a dataset
that has 500 cases,
that would be very
time-consuming to do.
And you could see
that this function of
computing this
variable can
save you a lot of time.
It's also more accurate.
It's going to
take any error
out of the equation.
And we know that often
when we do things by hand,
we can introduce
error into things,
so we want to avoid that.
That's one way to
computer a variable.
I'm going to show
you a different type
of variable that
we can compute.
I'm going to go
back to Transform,
I'm going to go back
to Compute Variable.
I'm actually going
to clear this out.
We're done with
someofitems,
we don't need to
worry about it,
we're not going to use
the same expression,
so I'm going to click
Reset in the bottom here.
So what I want
to do is create
the mean of the different
items that we have.
Sometimes if
you're working
with a pre-existing scale,
it might tell you to add
all the items
together and then
that's what represents
that theoretical concept
or that measure,
sometimes it might tell
you to use the mean.
So what I want to do
is compute both of
these things because they
both might be
helpful to me.
So what I'm going to do is
I'm going to type
meanofitems.
And again, that very
quickly lets me
differentiate between
sumofitems and
meanofitems.
Type & label, and again,
I'm just going to put
mean of items 1 through
6, click Continue.
Just like we did
before, click on All,
and then we're
going to go down
to mean, here's mean.
And when I click
on that, again,
it gives me that
sample text here.
This is very similar
to what we did before.
I'm going to click up, and
we're going to
kick over 1,
2, 3, 4, 5, and then 6.
I'm making sure to not
include this last
one, this sumofitems.
And then just
like last time,
we're going to delete out
that question mark,
that last comma.
We're going to
read through
it really quickly just
to avoid an error.
We've got a new
variable, meanofitems.
It's going to be
the mean of item 1,
2, 3, 4, 5, and 6.
I'm going to
click OK. SPSS
again showed me the
syntax of what it did.
I'm going to
minimize that.
And then here we have
the mean of items.
And if we really
quickly look at this,
I'm going to pick this
one, for example,
we've got 1,
1, 3, 3, 1, 2,
and a mean of 1.83 would,
just eyeballing
it, make sense.
If we look at this one,
3.67, 2,
3, 5, 4, 5, 3,
that would roughly
make sense
without having to
do the math of it,
but this has computed
the average score,
the mean score for all
six of those items.
So that is very
quickly how to
compute a new
variable in SPSS.
This is
particularly useful
when you have
collected data using
a pre-existing measure
and that measure has
instructed you to compute
the sum of items and
run your tests on that,
or maybe the mean of items
and run your
tests on that.
But this is a useful way
of understanding
how to create
new variables using
existing ones in SPSS.