Where to find the effect size in spss
Effect Size
I agree this is going to be the lesson
on performing effect size analyses we're
gonna specifically focus on the Cohen's
D effect size and the partial ADA
squared effect size so we have a data
set here with just three columns we have
participant ID some condition called
discussed condition and saying called
conservative attitudes imagine that in
the study individuals are brought into
the lab and they are asked to smell
something some individuals smell
something that has absolutely no sense
some individuals smell something that is
kind of floral smells nice while other
individuals smell something that smells
very very bad like rotten food if we go
to variable view we can see that a
disgust condition is saying called
manipulated disgust that's our
independent variable if we click on
values we can see that a negative one is
the pleasant to kind of floral smell the
zero is the control no disgust and the
one is the heinousness that's something
really nasty and then our dependent
variable is conservative attitudes do
people have more conservative attitudes
after smelling after being disgusted the
perhaps hypothesis is that they do so
we'll start off with a Cohen's D
analysis Cohen's D effect size is used
when you are comparing two groups so
let's say we want to perform an
independent sample t-test comparing the
the control group 0 and the disgust
group 1 so this is ignoring the negative
one the floral condition if we hit OK
and then we move a conservative at its
over here we'll run our independent
sample t-test we'll hit OK and we'll
find that in fact the groups do do
differ this is a significant difference
it's a T value of negative three point
seven eight two with ten degrees of
freedom and that's significant well
below the point zero five now if we look
at our means we can we'll use this for
determining our Cohen's D what we'll
need to do is we will go to an internet
browser and we will go to the following
address www
CCS edu backslash tilde faculty slash
Becker slash and it'll bring us to this
website which is an effect size
calculator this is a really good
calculator it allows you to calculate
Cohen's D in a number of ways we're
gonna see here we have group one mean
and Sand deviation and group two mean
and standard deviation so what we're
gonna do is we're gonna start inputting
these numbers the first mean it doesn't
matter which group is which we have a
mean of four with this information of
one point four one so we'll put in four
and one point four one and then for
group two it's a six point eight three
and one point one seven so six point
three and and if we hit compute we will
get our Cohen's D down here this
negative two point one according to
Cohen 0.2 0.2 0.3 is a small effect 0.5
is a moderate effect point eight is a
large effect so an effective two point
one or negative two point one would be
huge ignore the positive and negative we
take the absolute value so this would be
a very large effect and that's perhaps
not surprising given how big the means
are and the different thing that means
in this the relative small standard
deviation now let's say we wanted to
calculate partial a two squared which is
the effect size over a number of
variables are a number of different
levels not just two if we go back to our
data we can go to analyze general linear
model and univariate now you might be
thinking to yourself well we only have
one variable one independent variable
discuss why are we running a univariate
analysis why don't we just run a one-way
ANOVA well one way ANOVA doesn't give us
any options to calculate effect size so
we have to do a univariate analysis and
univariate analysis can be used for
one-way ANOVA is you can even use it for
T tests all univariate means is that you
have one dependent variable so the fact
that we tend to use you know independent
sample t-tests option when we do T tests
and the one way between solution over
option when we do one way between so
there's no but doesn't mean we couldn't
do
of area so we're gonna move manipulated
to discuss into fixed factors and
conservative attitudes into the
dependent variable and all we're gonna
do now is going to click on options and
we're gonna click on estimates of effect
size we can also click on descriptive
statistics if we want so you can find
that means and certain variations for
those groups we can hit ok and then ok
again we can see these are between
survey's factors there's six people in
each group here are the descriptive
statistics so it looks like there's a
difference between the three groups we
can go over to our between-subjects
effect test and see that the F is 5.9
where the significance of point 0 1 3
meaning that this is there is a
significant difference among all of the
groups we would write this as F 2 comma
15 equals five point nine zero three
comma P equals point zero one three the
partial eighth is squared however is
0.44 this would be a very large effect
and and this is how we get our partial a
2 squared which can be read and written
as as the ADA symbol squared equals
point four four zero and that is how you
calculate Cohen's D and partial 8a
squared in SPSS
