In this tutorial we're going to take a look at how to obtain means for
different groups of a variable on some other variable of interest.
Let me show you what I mean here. So, for example, in this data set, we have two
variables, play golf and satisfaction. Now play golf is coded, if I click on my
Value Labels button here, I've already coded it, and you can see that we have
either yes,
those who do play golf, or no, those who do not play golf. Now when I said I
wanted to obtain means for the different groups,
what I want is I want to get a mean on satisfaction this variable for golfers,
for those who answer yes to playing golf, I want a mean for this group alone, and
then I want to mean for the no group as well.
OK and this variable satisfaction, higher scores indicate greater satisfaction. And
these are 7 people who lived in the community in which there was a golf
course on it.
So 5 of the people who lived in the community who answered yes, they're
golfers, and the 2 who answered no, they are not golfers.
OK so once again I want satisfaction, a mean satisfaction level, separately for
the yes group and one for the no group;
I want it separated. OK and this is often area of confusion in SPSS, how to do
this.
Let's go ahead and proceed with perhaps a normal route of trying to figure this
out. Go to Analyze, Descriptive Statistics, Descriptives, and we're going
to see what happens if we just go ahead and do an analysis directly on
satisfaction. OK so I'm going to move satisfaction over,
go to Options, and then I want the Mean and let's get the Standard Deviation as
well for this lesson, so I'll be deselect Minimum and Maximum. Click Continue and
click OK. Our output or viewer window opens
and notice here in our Descriptive Statistics, recall that I said that I
wanted means separately for the yes group and the no group. But if you notice
this output here, I have satisfaction
all 7 people are included, and I have just one overall mean of 7.86, so this
actually didn't give me means for the different groups. I don't have a mean for
the yes and a mean for the no groups.
I just have an overall mean. So this actually didn't do what I wanted.
So let's go try again. Let's click on this little star here, this
this will take you straight to the data. And, once again, I want a mean for just
the yes group, the 1s, and a mean for just the 2, the No's. And I wanted to
show you the Descriptives way just to show you that it's not actually correct,
and why it's not. So now we know what we want,
we want the means broken down separately by the different groups. To do that we
need to go to Analyze, Compare Means, Means. OK so select that and then here in
our Dependent List,
this is where the satisfaction variable would go, so move that over. And the
Independent List will always be the categorical variable, in this case the
variable, play golf.
It's categorical and it happens to be dichotomous because there are only two
options, a 1 or a 2, or a Yes
or No. OK so play golf will go to the Independent List and then go to Options,
so we can see what options are selected.
I see a mean and I see a standard deviation by default and number of cases
as well. We can keep number of cases, that could be helpful, but let's drag that up
to the top here and have that present first in our output. OK so
everything looks good here.
Let's click Continue and then click OK. Now our output opens
we're going to scroll down here, actually I'm going to delete a little bit of this.
I'll delete this by selecting it, pressing the Delete key. I'm going to
delete this here, so we can see these two tables at the same time.
Here's the output of my Means procedure, the procedure we just ran.
I'm just going to briefly mention this Case Processing Summary table, just to
say it shows that all 7 observations were included, and none were excluded, so
everything was analyzed, that's all that means.
Zeroing in on this table, the Report table,
this is what we want to see. Notice here I have the play golf variable and I have
analyses for the Yes group the 5 people who were in the Yes group, and the
No group, the two people in that group. And notice now I have means broken down
separately for these two groups, which is exactly what I wanted.
So the yes group, those who play golf, had an average satisfaction score of 8.20,
whereas those who did not play golf had an average satisfaction score of 7.00.
So you should be able to see, at least in the sample here, that those who played golf
did have a higher average satisfaction score, or higher mean satisfaction score,
than those who did not play golf. OK and we see the standard deviations here as well.
Just as a side note this standard deviation is 0 because our two people
who were in the No group both had a score of 7.
If they both have a score 7, there's no variability at all in the data set for
this group.
So that's why we have a standard deviation of 0. One last note here.
Notice the Total. See where it says 7 here, and then we have a mean of
7.86 standard deviation .90? If we go back up here to our original analysis,
the analysis using Descriptive Statistics and then using the
Descriptives option,
notice we have the same thing: 7.86 for the mean .90 for the standard
deviation.
So what the Means procedure does down here
it breaks it down by the different groups, and it also gives you the overall
analysis down here, which is what we got the first time by Descriptive Statistics.
But anytime you want to get a mean, a descriptive analysis, but of means
separately for different groups, you want to go to Analyze, Compare Means and then
the Means procedure. Now if you're doing inferential analyses, like a two-way
ANOVA, for example, you can get that within the two-way ANOVA procedure.
But if we're just doing simple descriptive statistics, no inferential
testing, and we just want to see means here by different groups then you want
to use Analyze, Compare Means, Means. This concludes the tutorial on using the
Means procedure in SPSS.