Question 5: Returning to the head circumference data, delete the invalid observations. Now compute the difference between the two measurements of head circumference.
We compute the difference by Transform, Compute, then type 'difference' into Target variable. Select variable head circ 1 and put it into the numerical expression. Type '-'. Select variable head circ 2 and put it into the numerical expression. You should now have head circ 1 - head circ 2. Click OK.
A new variable 'difference' should now appear in the SPSS Data Editor.
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