Dear all,
I am trying to use EM (Expectation-Maximization) to impute the missing
values in a set of 9 test scores. Is there anyone out there who can help
me with this? I am using SPSS 12.01.
The descriptives for the test scores are as follows:
Descriptive Statistics
N
Minimum
Maximum
Mean
Std. Deviation
1T Problem Arithmetic Test score
10816
0
10
5.19
2.440
1T Southgate Group Reading Test score
10842
0
30
23.76
6.764
1T Draw-a-man test score
10641
0
53
24.02
6.955
1S Total score on Copying Designs Test
10808
0
12
7.08
1.949
2T Verbal score on general ability test
10604
0
40
22.53
9.174
2T Non verbal score on gen ability test
10604
0
40
21.26
7.385
2T Total score on general ability test
10604
0
80
43.79
15.710
2T Reading comprehension test score
10602
0
35
16.27
6.151
2T Mathematics test score
10598
0
40
17.13
10.254
Valid N (listwise)
9365
Under 'Distribution' there are 3 options: 1. normal, 2. mixed normal,
and 3. Student's t. For a mixed normal assumption, you have to specify
the proportion and the standard deviation ratio. For Student's t
distribution, you must specify the degrees of freedom. How do I decide
which one to choose?
I started out by trying option 1 - normal. Here is the syntax:
MVA
n90 n92 n1840 n914 n917 n920 n923 n926 n457
/EM ( TOLERANCE=0.001 CONVERGENCE=0.0001 OUTFILE='F:\Work
Alice\coeducation vs single sex\academic attainment\test scores EM
imputation.sav' ) .
EXECUTE.
When I looked at the descriptives for the resulting dataset, I found
that some of the variables now included minus values, whereas all the
original variables had ranges starting with zero. Why would this be?
Also, I can't work out how to get the serial number included in the new
outfile - without which I can't reattach the new variables to the rest
of my dataset.
Many thanks in advance for any responses!
Alice
Dr Alice Sullivan
Institute of Education
London
020 76126661
[hidden email]
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