Summing partially missing cases in SPSS
The default for obtaining sums and means in SPSS is to work them out only for cases with complete data.
To sum over cases, with at least x complete variable values in SPSS, we use the function, sum.x. Similarly to obtain the mean for cases, with at least x complete variable values, we use mean.x. e.g.
compute scoresum = sum.3(a,b,c). compute scoremn = mean.2(a,b,c). exe.
scoresum will return missing for cases with <3 non-missing values. Ie any non-missing a, b and c. scoremn will return missing for cases with <2 non-missing values, ie having two or three missing values of any of variables a or b or c.