Interpreting statistical tests in Psychology
Summary of test

Spearman’s 
rho




Chi square




Mann
Whitney U




Wilcoxon T


A test of
association
used with a
correlational
study
nothing is
manipulated
with ordinal data
A test of
association
used with
nominal data
where
frequencies of
mutually
exclusive
categories are
observed
nothing is
manipulated
used with an
experiment
with
independent
groups design
(unrelated data)
requiring a test
of difference
on ordinal data
used with an
experiment
with repeated
measures design
(sometimes
called related
data)
requiring a test
of difference
on ordinal data
Does observed
value need to
be ≥ or ≤
critical value
to be
significant?*
What you do to establish whether your
observed value is significant


rho≥C



x²≥C

First identify your observed value of chi
square
Then calculate your degrees of freedom
by multiplying (rows -1) x (columns -1)
Then, in the table of critical values, find
the critical value for:
 the degrees of freedom that you
have
 the level of significance indicated
 whether you have a one- or twotailed test

First identify the observed value of U (the
lower total number of points)
 whether you have a one- or twotailed test
 the level of significance indicated
 In the table of critical values, find
the value for the number of Ps in
group 1 (N1) and the number of
Ps in group 2 (N2)
 Compare this value (your
observed value) of U to the
critical value


Identify the observed value of T
Then, in the table of critical values, find
the critical value for:
 the level of significance indicated
 whether you have a one- or twotailed test
 compare your observed value of
T to the critical value
U≤C
T≤C
First identify your observed value of rho
Then, in the table of critical values, find
the critical value for:
 the number of pairs of
observations (N) that you have
 the level of significance indicated
 whether you have a one- or twotailed test
compare your observed value of rho to
the critical value