The relative efficiency (RE) of using the finite m imputation estimator, rather than using an infinite number for the fully efficient imputation, in units of variance, is approximately a function of m and (Rubin 1987, p. 114):
Table 76.2 shows relative efficiencies with different values of m and .
Table 76.2: Relative Efficiencies



m 
10% 
20% 
30% 
50% 
70% 

3 
0.9677 
0.9375 
0.9091 
0.8571 
0.8108 

5 
0.9804 
0.9615 
0.9434 
0.9091 
0.8772 

10 
0.9901 
0.9804 
0.9709 
0.9524 
0.9346 

20 
0.9950 
0.9901 
0.9852 
0.9756 
0.9662 
The table shows that for situations with little missing information, only a small number of imputations are necessary. In practice, the number of imputations needed can be informally verified by replicating sets of m imputations and checking whether the estimates are stable between sets (Horton and Lipsitz 2001, p. 246).