The MI Procedure

FREQ Statement
FREQ variable ;

If one variable in your input data set represents the frequency of occurrence of other values in the observation, specify the variable name in a FREQ statement. PROC MI then treats the data set as if each observation appears times, where is the value of the FREQ variable for the observation. If the value of the FREQ variable is less than one, the observation is not used in the analysis. Only the integer portion of the value is used. The total number of observations is considered to be equal to the sum of the FREQ variable when PROC MI calculates significance probabilities.