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Example 3
E In the Files of type list, select Text (*.txt), select Attg_old.txt, and then click Open.
E In the Data Files dialog box, click OK.
Testing a Hypothesis That Two Variables Are Uncorrelated
Among Attig’s 40 old subjects, the sample correlation between age and vocabulary is
–0.09 (not very far from 0). Is this correlation nevertheless significant? To find out, we
will test the null hypothesis that, in the population from which these 40 subjects came,
the correlation between age and vocabulary is 0. We will do this by estimating the
variance-covariance matrix under the constraint that age and vocabulary are
uncorrelated.
Specifying the Model
Begin by drawing and naming the two observed variables, age and vocabulary, in the
path diagram, using the methods you learned in Example 1.
Amos provides two ways to specify that the covariance between age and vocabulary
is 0. The most obvious way is simply to not draw a double-headed arrow connecting
the two variables. The absence of a double-headed arrow connecting two exogenous
variables implies that they are uncorrelated. So, without drawing anything more, the